View source for Primary color

{{Short description|Fundamental color in color mixing}}
{{About|colors|other uses|Primary Colors (disambiguation){{!}}Primary Colors}}
{{Use American English|date=October 2020}}
[[File:CRT phosphors.png|right|thumb|upright=1.75|The [[emission spectra]] of the three [[phosphor]]s that define the '''additive primary colors''' of a [[cathode-ray tube|CRT]] color video display. Other electronic color display technologies ([[LCD]], [[Plasma display]], [[OLED]]) have analogous sets of primaries with different emission spectra.]]

'''Primary colors''' are [[colorant]]s or coloured [[light]]s that can be mixed in varying amounts to produce a [[gamut]] of [[colors]]. This is the essential method used to create the perception of a broad range of colors in, e.g., electronic displays, color printing, and paintings. Perceptions associated with a given combination of primary colors can be predicted by an appropriate mixing model (e.g., [[additive mixing|additive]], [[subtractive mixing|subtractive]]) that uses the physics of how light interacts with physical media, and ultimately the [[retina]] to be able to accurately display the intended colors. 

The most common colour mixing models are the additive primary colors (red, green, blue) and the subtractive primary colors (cyan, magenta, yellow). Red, yellow, and blue are also [[#Red, yellow, and blue as primary colors|commonly taught as primary colors]] (usually in the context of subtractive color mixing as opposed to additive color mixing), despite some criticism due to its lack of scientific basis.

Primary colours can also be conceptual (not necessarily real), either as additive mathematical elements of a [[color space]] or as irreducible phenomenological categories in domains such as psychology and [[Philosophy of color|philosophy]]. Color space primaries are precisely defined and empirically rooted in [[psychophysics|psychophysical]] [[colorimetry]] experiments which are foundational for understanding [[color vision]]. Primaries of some color spaces are ''complete'' (that is, all visible colors are described in terms of their primaries weighted by nonnegative primary intensity coefficients) but necessarily ''imaginary''<ref name="handprintprimaries">Bruce MacEvoy.  "Do 'Primary' Colors Exist?" ([http://www.handprint.com/HP/WCL/color6.html#imaginary imaginary or imperfect primaries section] {{Webarchive|url=https://web.archive.org/web/20080717034228/http://www.handprint.com/HP/WCL/color6.html#imaginary |date=17 July 2008 }}).  ''Handprint''.  Accessed 10 August 2007.</ref> (that is, there is no plausible way that those primary colors could be represented physically, or perceived). Phenomenological accounts of primary colors, such as the psychological primaries, have been used as the conceptual basis for practical color applications even though they are not a quantitative description in and of themselves.

[[set (mathematics)|Sets]] of color space primaries are generally ''arbitrary'', in the sense that there is no one set of primaries that can be considered the canonical set. Primary pigments or light sources are selected for a given application on the basis of subjective preferences as well as practical factors such as cost, stability, availability etc.

The concept of primary colors has a long, complex history. The choice of primary colors has changed over time in different domains that study color. Descriptions of primary colors come from areas including philosophy, art history, color order systems, and scientific work involving the physics of light and perception of color.

Art education materials commonly use red, yellow, and blue as primary colors, sometimes suggesting that they can mix all colors. No set of real colorants or lights can mix all possible colors, however. In other domains, the three primary colors are typically red, green and blue, which are more closely aligned to the sensitivities of the [[photopigment|photoreceptor pigments]] in the [[cone cell]]s.<ref>[https://science.howstuffworks.com/primary-colors.htm Primary Colors Are Red, Yellow and Blue, Right? Well, Not Exactly], ''HowStuffWorks''</ref><ref>[https://www.olympus-lifescience.com/en/microscope-resource/primer/lightandcolor/primarycolorsintro/ Introduction to the Primary Colors], ''Olympus Life Science''</ref>

== Color model primaries ==

A [[color model]] is an abstract model intended to describe the ways that colors behave, especially in [[color mixing]]. Most color models are defined by the interaction of multiple primary colors. Since most humans are [[trichromacy|trichromatic]], color models that want to [[color reproduction|reproduce]] a meaningful portion of a human's perceptual [[gamut]] must use at least ''three'' primaries.<ref>{{cite book |last1=Westland |first1=Stephen |last2=Cheung |first2=Vien |editor1-last=Chen |editor1-first=Janglin |editor2-last=Cranton |editor2-first=Wayne |editor3-last=Fihn |editor3-first=Mark |title=Handbook of visual display technology |date=2012 |publisher=Springer |location=Cham, Switzerland |isbn=978-3-540-79567-4 |page=155 |edition=2nd|quote="Color vision is based upon the responses of three classes of cones in the retina, each of which has broadband sensitivity but maximum sensitivity at different wavelengths. A consequence of this is that color reproduction is trichromatic – the use of three primaries allows a wide range of colors to be reproduced."}}</ref> More than three primaries are allowed, for example, to increase the size of the gamut of the color space, but the entire human perceptual gamut can be reproduced with just three primaries (albeit imaginary ones as in the [[CIE XYZ color space]]).

Some humans (and most mammals<ref>{{cite journal |last1=Bowmaker |first1=James K |title=Evolution of colour vision in vertebrates |journal=Eye |date=May 1998 |volume=12 |issue=3 |page=543 |doi=10.1038/eye.1998.143|pmid=9775215 |doi-access=free }}</ref>) are [[dichromacy|dichromats]], corresponding to specific forms of [[color blindness]] in which color vision is mediated by only two of the types of color receptors. Dichromats require only two primaries to reproduce their entire gamut and their participation in color matching experiments was essential in the determination of cone fundamentals leading to all modern color spaces.<ref>{{cite book |last1=Stockman |first1=Andrew |title=Encyclopedia of Color Science and Technology |chapter=Cone Fundamentals |date=2016 |pages=541–546 |doi=10.1007/978-1-4419-8071-7_85|isbn=978-1-4419-8070-0 }}</ref> Despite most vertebrates being [[tetrachromacy|tetrachromatic]],<ref>{{cite journal |last1=Scholtyßek |first1=C. |last2=Kelber |first2=A. |title=Farbensehen der Tiere: Von farbenblinden Seehunden und tetrachromatischen Vögeln |journal=Der Ophthalmologe |date=November 2017 |volume=114 |issue=11 |pages=978–985 |doi=10.1007/s00347-017-0543-6|pmid=28752388 |doi-access=free }}</ref> and therefore requiring four primaries to reproduce their entire gamut, there is only one scholarly report of a functional human [[tetrachromacy|tetrachromat]], for which trichromatic color models are insufficient.<ref>{{cite journal
| last1   = Jordan
| first1  = G.
| last2   = Deeb
| first2  = S. S.
| last3   = Bosten
| first3  = J. M.
| last4   = Mollon
| first4  = J. D.
| title   = The dimensionality of color vision in carriers of anomalous trichromacy
| journal = Journal of Vision
| date    = 20 July 2010
| volume  = 10
| issue   = 8
| page   = 12
| doi     = 10.1167/10.8.12
| pmid = 20884587
| doi-access= free
}}</ref>

=== Additive models ===
{{See also|RGB color model}}
[[File:AdditiveColor.svg|thumb|Additive primary color model]]
[[File:LCD pixels RGB.jpg|thumb|upright=1.4|A photograph of the red, green, and blue elements (subpixels) of an [[Liquid-crystal display|LCD]]. Additive mixing explains how light from these colored elements can be used for photorealistic color image reproduction.]]

The perception elicited by multiple light sources co-stimulating the same area of the retina is [[additive color|additive]], i.e., predicted via summing the [[spectral power distribution]]s (the intensity of each wavelength) of the individual light sources assuming a color matching context.<ref name="Williamson1983">{{cite book |last1=Williamson |first1=Samuel J. |title=Light and color in nature and art |date=1983 |publisher=Wiley |location=New York |isbn=0-471-08374-7 |url=https://archive.org/details/lightcolorinnatu00will/page/17/mode/2up |access-date=28 April 2021}}</ref>{{rp|17–22}} For example, a [[purple]] spotlight on a dark background could be matched with coincident [[blue]] and [[red]] spotlights that are both dimmer than the purple spotlight. If the intensity of the purple spotlight was doubled it could be matched by doubling the intensities of both the red and blue spotlights that matched the original purple. The principles of additive color mixing are embodied in [[Grassmann's law (optics)|Grassmann's laws]].<ref>{{cite book
| last1      = Reinhard
| first1     = Erik
| last2      = Khan
| first2     = Arif
| last3      = Akyuz
| first3     = Ahmet
| last4      = Johnson
| first4     = Garrett
| title      = Color imaging: fundamentals and applications
| date       = 2008
| publisher  = A.K. Peters
| location   = Wellesley, Mass
| isbn       = 978-1-56881-344-8
| pages      = 364–365
| url        = https://books.google.com/books?id=suLqBgAAQBAJ&q=grassman%27s+laws+additive&pg=PA364
| access-date = 31 December 2017
}}</ref> Additive mixing is sometimes described as "additive color matching"<ref>{{cite book |last1=Berns |first1=Roy S. |title=Billmeyer and Saltzman's principles of color technology |date=2019 |location=Hoboken, NJ |isbn=978-1-119-36719-2 |pages=54–64 |edition=Fourth}}</ref> to emphasize the fact the predictions based on additivity only apply assuming the color matching context. Additivity relies on assumptions of the color matching context such as the match being in the [[Fovea centralis|foveal]] field of view, under appropriate luminance, etc.<ref>{{cite book |last1=Brill |first1=Michael H. |last2=Robertson |first2=Alan R. |chapter=Open Problems on the Validity of Grassmann's Laws |title=Colorimetry |date=27 July 2007 |pages=245–259 |doi=10.1002/9780470175637.ch10|isbn=978-0-470-17563-7 | quote="Grassmann's laws are known not to be exactly true in human color matching. Symmetry could be called into question by color difference formulas, such as CIE94,3 that are asymmetric between batch and standard. Transitivity can be considered to be violated if we take the term ''color match'' to mean that two colors are within a just-noticeable difference of each other. In this case, adding two subthreshold differences together could produce a combined difference that is above thresh- old. Proportionality and additivity can also be compromised. Besides the three cone types that herald the trichromacy of vision at high (photopic) light intensities, a fourth photoreceptor type (rods) contributes to vision at low (mesopic and scotopic) light intensities and away from the center of vision (fovea). At very high light intenities, unbleached photopigments deplete and, in aggregate, change their action spectrum. At still higher light intensities, a photopigment molecule can absorb multiple photons but respond as if it absorbed only one photon. All these effects compromise Grassmann's laws, but the successful application of the laws, for example, in photography and television, has led us to believe that the compromises are not serious."}}</ref>

Additive mixing of coincident spot lights was applied in the experiments used to derive the [[CIE 1931]] colorspace (see [[#Color space primaries|color space primaries section]]). The original ''[[monochromatic radiation|monochromatic]]'' primaries of the wavelengths of 435.8&nbsp;nm ([[violet (color)|violet]]), 546.1&nbsp;nm ([[green]]), and 700&nbsp;nm (red) were used in this application due to the convenience they afforded to the experimental work.<ref>{{cite journal
| last1   = Fairman
| first1  = Hugh S.
| last2   = Brill
| first2  = Michael H.
| last3   = Hemmendinger
| first3  = Henry
| title   = How the CIE 1931 color-matching functions were derived from Wright-Guild data
| journal = Color Research & Application
| date    = February 1997
| volume  = 22
| issue   = 1
| pages   = 11–23
| doi     = 10.1002/(SICI)1520-6378(199702)22:1<11::AID-COL4>3.0.CO;2-7
| quote = "The first of the resolutions offered to the 1931 meeting defined the color-matching functions of the soon-to-be-adopted standard observer in terms of Guild's spectral primaries centered on wavelengths 435.8, 546.1, and 700nm. Guild approached the problem from the viewpoint of a standardization engineer. In his mind, the adopted primaries had to be producible with national-standardizing-laboratory accuracy. The first two wavelengths were mercury excitation lines, and the last named wavelength occurred at a location in the human vision system where the hue of spectral lights was unchanging with wavelength. Slight inaccuracy in production of the wavelength of this spectral primary in a visual colorimeter, it was reasoned, would introduce no error at all."
}}</ref>

Small red, green, and blue elements (with controllable brightness) in electronic displays mix additively from an appropriate viewing distance to synthesize compelling colored images. This specific type of additive mixing is described as ''partitive mixing''.<ref name="Williamson1983"/>{{rp|21–22}} Red, green, and blue light are popular primaries for partitive mixing since primary lights with those hues provide a large [[color triangle]] ([[gamut]]).<ref>{{cite book |last1=Tooms |first1=Michael S. |title=Colour Reproduction in Electronic Imaging Systems: Photography, Television, Cinematography |date=26 January 2016 |publisher=John Wiley & Sons |isbn=978-1-119-02176-6 |page=22 |url=https://books.google.com/books?id=nQslCgAAQBAJ |access-date=25 February 2021 |language=en |quote=If we now define the primaries in terms of the three colours which together in various ratios produce the largest gamut of colours in the eye–brain complex, then, as reasoned above, the primary colours are red, green and blue.}}</ref>

The exact colors chosen for additive primaries are a compromise between the available technology (including considerations such as cost and power usage) and the need for large chromaticity gamut. For example, in 1953 the [[NTSC]] specified primaries that were representative of the [[phosphor]]s available in that era for color [[Cathode-ray tube|CRT]]s. Over decades, market pressures for brighter colors resulted in CRTs using primaries that deviated significantly from the original standard.<ref>{{cite web |last1=Poynton |first1=Charles |title=Frequently Asked Questions about Color |url=http://poynton.ca/PDFs/ColorFAQ.pdf |archive-url=https://web.archive.org/web/20180219004614/http://poynton.ca/PDFs/ColorFAQ.pdf |archive-date=2018-02-19 |url-status=live |website=Charles Poynton, PhD |access-date=26 April 2021 |quote=The NTSC in 1953 specified a set of primaries that were representative of phosphors used in color CRTs of that era. But phosphors changed over the years, primarily in response to market pressures for brighter receivers, and by the time of the first the videotape recorder the primaries in use were quite different from those "on the books". So although you may see the NTSC primary chromaticities documented, they are of no use today.}}</ref> Currently, [[Rec. 709|ITU-R BT.709-5]] primaries are typical for [[high-definition television]].<ref>{{cite book |last1=Westland |first1=Stephen |last2=Cheung |first2=Vien |editor1-last=Chen |editor1-first=Janglin |editor2-last=Cranton |editor2-first=Wayne |editor3-last=Fihn |editor3-first=Mark |title=Handbook of visual display technology |date=2016 |publisher=Springer |location=Cham, Switzerland |isbn=978-3-319-14347-7 |pages=171–177 |edition=2nd}}</ref>
{{clear}}

=== Subtractive models ===
{{See also|CMYK color model}}
[[File:SubtractiveColor.svg|thumb|Subtractive primary color model]]
[[File:Halftoningcolor.svg|thumb|upright=1.4|A magnified representation of small partially overlapping spots of cyan, magenta, yellow, and key (black) [[halftone]]s in [[CMYK]] process printing. Each row represents the pattern of partially overlapping ink "rosettes" so that the patterns would be perceived as blue, green, and red when viewed on white paper from a typical viewing distance. The overlapping ink layers mix subtractively while additive mixing predicts the color appearance from the light reflected from the rosettes and white paper in between them.]]

The [[subtractive color]] mixing model predicts the resultant spectral power distribution of light filtered through overlaid partially absorbing materials, usually in the context of an underlying reflective surface such as white paper.<ref name="Williamson1983"/>{{rp|22–23}}<ref>{{cite book |last1=Berns |first1=Roy S. |title=Billmeyer and Saltzman's Principles of Color Technology |date=9 April 2019 |publisher=John Wiley & Sons |isbn=978-1-119-36722-2 |pages=195–209 |url=https://books.google.com/books?id=8GGLDwAAQBAJ |language=en}}</ref> Each layer partially absorbs some wavelengths of light from the illumination while letting others pass through, resulting in a colored appearance. The resultant spectral power distribution is predicted by the wavelength-by-wavelength product of the spectral reflectance of the illumination and the product of the spectral reflectances of all of the layers.<ref>{{cite web |last1=Levoy |first1=Marc |title=Additive versus subtractive color mixing |url=https://graphics.stanford.edu/courses/cs178-10/applets/colormixing.html |website=graphics.stanford.edu |access-date=4 November 2020 |quote="On the other hand, if you reflect light from a colored surface, or if you place a colored filter in front of a light, then some of the wavelengths present in the light may be partially or fully absorbed by the colored surface or filter. If we characterize the light as an SPD, and we characterize absorption by the surface or filter using a spectrum of reflectivity or transmissivity, respectively, i.e. the percentage of light reflected or transmitted at each wavelength, then the SPD of the outgoing light can be computed by multiplying the two spectra. This multiplication is (misleadingly) called subtractive mixing."}}</ref> Overlapping layers of ink in printing mix subtractively over reflecting white paper, while the reflected light mixes in a partitive way to generate color images.<ref name="Williamson1983"/>{{rp|30–33}}<ref>{{cite journal |last1=Kuehni |first1=Rolf |title=Color mixture |journal=Scholarpedia |date=2011 |volume=6 |issue=1 |article-number=10686 |doi=10.4249/scholarpedia.10686|bibcode=2011SchpJ...610686K |doi-access=free }}</ref> Importantly, unlike additive mixture, the color of the mixture is not well predicted by the colors of the individual dyes or inks. The typical number of inks in such a printing process is 3 (CMY) or 4 ([[CMYK]]), but can commonly range to 6 (e.g., [[hexachrome|Pantone hexachrome]]). In general, using fewer inks as primaries results in more economical printing but using more may result in better color reproduction.<ref>{{cite book |last1=Sharma |first1=Abhay |title=Understanding color management |date=2018 |location=Hoboken, NJ |isbn=978-1-119-22363-4 |page=235 |edition=2nd}}</ref>

[[Cyan]] (C), [[magenta]] (M), and [[yellow]] (Y) are good chromatic subtractive primaries in that filters with those colors can be overlaid to yield a surprisingly large chromaticity gamut.<ref>{{cite book |last1=Westland |first1=Stephen |last2=Cheung |first2=Vien |editor1-last=Chen |editor1-first=Janglin |editor2-last=Cranton |editor2-first=Wayne |editor3-last=Fihn |editor3-first=Mark |title=Handbook of visual display technology |date=2012 |publisher=Springer |location=Cham, Switzerland |isbn=978-3-540-79567-4 |page=155 |edition=2nd|quote="The optimum primaries of the subtractive color system are cyan, magenta, and yellow. The use of cyan, magenta, and yellow subtractive primaries allows a surprisingly large – albeit limited – gamut of colors to be reproduced."}}</ref> A black (K) ink (from the older "[[key plate]]") is also used in CMYK systems to augment C, M and Y inks or dyes: this is more efficient in terms of time and expense and less likely to introduce visible defects.<ref>{{cite web |last1=Poynton |first1=Charles |title=Color FAQ - Frequently Asked Questions Color |url=https://poynton.ca/notes/colour_and_gamma/ColorFAQ.html#RTFToC25 |website=poynton.ca | quote=Printing black by overlaying cyan, yellow and magenta ink in offset printing has three major problems. First, coloured ink is expensive. Replacing coloured ink by black ink – which is primarily carbon – makes economic sense. Second, printing three ink layers causes the printed paper to become quite wet. If three inks can be replaced by one, the ink will dry more quickly, the press can be run faster, and the job will be less expensive. Third, if black is printed by combining three inks, and mechanical tolerances cause the three inks to be printed slightly out of register, then black edges will suffer coloured tinges. Vision is most demanding of spatial detail in black and white areas. Printing black with a single ink minimizes the visibility of registration errors. |access-date=27 April 2021}}</ref> Before the color names ''cyan'' and ''magenta'' were in common use, these primaries were often known as blue and red, respectively, and their exact color has changed over time with access to new pigments and technologies.<ref>{{cite book
| title     = General Physics and Its Application to Industry and Everyday Life
| author    = Ervin Sidney Ferry
| publisher = John Wiley & Sons
| year      = 1921
| url       = https://books.google.com/books?id=3rYXAAAAIAAJ&q=date:0-1923+additive+color+mixing+primary&pg=PA621
}}</ref> Organizations such as [[Fogra]],<ref>{{cite web |title=FOGRA characterization data |url=https://www.color.org/chardata/fogra.xalter |website=International Color Consortium |access-date=26 April 2021}}</ref> [[European Color Initiative]] and [[Specifications for Web Offset Publications|SWOP]] publish [[colorimetry|colorimetric]] CMYK standards for the printing industry.<ref>{{cite book |last1=Homann |first1=Jan-Peter |title=Digital color management: principles and strategies for the standardized print production |date=2009 |publisher=Springer |location=Berlin |isbn=978-3-540-69377-2}}</ref>
{{clear}}

== Traditional red, yellow, and blue primary colors as a subtractive system ==
[[File:Color Mixing Guide cover and plates.jpg|thumb|upright=1.4|Color Mixing Guide, John L. King 1925, cover and plates describing yellow, red, and blue color mixing]]
[[File:Farbkreis Itten 1961.svg|thumb|upright=0.8|A representation of [[Johannes Itten]]'s color wheel showing his red, yellow, and blue as primary colors within the central equilateral triangle<ref name="itten1961"/>]]

Color theorists since the seventeenth century, and many artists and designers since that time, have taken red, yellow, and blue to be the primary colors (see [[#Red,_yellow,_and_blue_as_primary_colors|history]] below). This RYB system, in "traditional color theory", is often used to order and compare colors, and sometimes proposed as a system of mixing pigments to get a wide range of, or "all", colors.<ref name="o'connor">
O'Connor, Zena. "Traditional colour theory: A review." Color Research & Application, 8 January 2021.
</ref>
O'Connor describes the role of RYB primaries in traditional color theory:<ref>
{{cite book | title=Encyclopedia of Color Science and Technology – Living Edition |publisher=Springer |chapter-url=https://link.springer.com/referenceworkentry/10.1007/978-3-642-27851-8_453-1 |access-date=6 June 2021 | author = Zena O'Connor | chapter = RYB Color|year=2021 |pages=1–4 |doi=10.1007/978-3-642-27851-8_453-1 |isbn=978-3-642-27851-8 |s2cid=241083080 }}
</ref>
{{blockquote|A cornerstone component of traditional color theory, the RYB conceptual color model underpins the notion that the creation of an exhaustive gamut of color nuances occurs via intermixture of red, yellow, and blue pigments, especially when applied in conjunction with white and black pigment color. In the literature relating to traditional color theory and RYB color, red, yellow, and blue are often referred to as primary colors and represent exemplar hues rather than specific hues that are more pure, unique, or proprietary variants of these hues.}}

Traditional color theory is based on experience with pigments, more than on the science of light. In 1920, Snow and Froehlich explained:<ref>{{cite book | author=Bonnie E. Snow and Hugo B. Froehlich |title=The Theory and Practice of Color |date=1920 |publisher=Prang |page=14 |url=https://books.google.com/books?id=-_kjAAAAMAAJ&q=snow+%22the+theory+and+practice+of+color%22 |access-date=12 June 2021}}</ref>
{{blockquote
|text=It does not matter to the makers of dyes if, as the physicist says, red light and green light in mixture make yellow light, when they find by experiment that red pigment and green pigment in mixture produce gray.  No matter what the spectroscope may demonstrate regarding the combination of yellow rays of light and blue rays of light, the fact remains that yellow pigment mixed with the blue pigment produces green pigment.}}

The widespread adoption of teaching of RYB as primary colors in post-secondary art schools in the twentieth century has been attributed to the influence of the [[Bauhaus]], where [[Johannes Itten]] developed his ideas on color during his time there in the 1920s, and of his book on color<ref>
{{cite journal |last1=Gage |first1=John |title=Colour at the Bahaus |journal=AA Files |date=1982 |issue=2 |pages=50–54 |jstor=29543325 |issn=0261-6823}}
</ref><ref>
{{cite journal |last1=Raleigh |first1=Henry P. |title=Johannes Itten and the Background of Modern Art Education |journal=Art Journal |date=1968 |volume=27 |issue=3 |pages=284–302 |doi=10.2307/775089|jstor=775089 }}</ref> published in 1961.<ref name="itten1961">{{cite book |last1=Itten |first1=Johannes |title=The art of color: the subjective experience and objective rationale of color |date=1961 |publisher=Reinhold Pub. Corp |location=New York |isbn=0-442-24037-6 |pages=34–37 |quote=By way of introduction to color design, let us develop the 12-hue color circle from the primaries{{snd}} yellow, red, and blue. As we know, a person with normal vision can identify a red that is neither bluish, nor yellowish; a yellow that is neither greenish, nor reddish: and a blue that is neither greenish, nor reddish. In examining each color, it is important to view it against a neutral-gray background.}}
</ref>

In discussing color design for the web, Jason Beaird writes:<ref>{{cite web|title=Rethinking Web Color: Classical Color Wheels for Modern Digital Design|url=https://www.josant-tools.net/p/rethink-web-color.html}}</ref> 
{{blockquote
|text=The reason many digital artists still keep a red, yellow, and blue color wheel handy is because the color schemes and concepts of traditional color theory are based on that model.&nbsp;... Even though I design mostly for the Web—a medium that's displayed in RGB—I still use red, yellow, and blue as the basis for my color selection.  I believe that color combinations created using the red, yellow, and blue color wheel are more aesthetically pleasing, and that good design is about aesthetics.}}

As with any system of real primaries, not all colors can be mixed from RYB primaries.<ref>
{{cite book
| last1  = Westland
| first1 = Stephen
| title  = Handbook of Visual Display Technology |date=2016
| publisher = Springer International Publishing
| page = 162
| url = https://rd.springer.com/content/pdf/10.1007/978-3-319-14346-0_11.pdf
| access-date = 12 December 2017
| language = en
| doi = 10.1007/978-3-319-14346-0_11
| isbn = 978-3-319-14346-0
| quote = A common misapprehension is that it is possible to define three color primaries that could create any color by mixture. Unfortunately, the range of reproducible colors (or gamut) for a trichromatic additive (or subtractive) system is limited and is always smaller than the gamut of all the colors possible in the world. However, the gamut is smaller or larger depending upon the choice of primaries. Pragmatically, for additive color mixing the largest gamut is achieved when the primaries are red, green, and blue.
}}
</ref> 
For example, if the blue pigment is a deep [[Prussian blue]], then a muddy desaturated green may be the best that can be had by mixing with yellow.<ref name=stjohn/> To achieve a larger gamut of colors via mixing, the blue and red pigments used in illustrative materials such as the ''Color Mixing Guide'' in the image are often closer to [[peacock blue]] (a [[blue-green]] or [[cyan]]) and [[carmine (color)|carmine]] (or [[crimson]] or [[magenta]]) respectively.<ref name=stjohn>
{{cite journal |last1=St. John |first1=Eugene |title=Some Practical Hints on Presswork |journal=The Inland Printer |date=February 1924 |volume=72 |issue=5 |page=805 |url=https://books.google.com/books?id=nxUhAQAAMAAJ&pg=RA8-PA805 | quote = While Prussian blue and crimson lake are available in three-color work, a broken yellow like Dutch pink is not, unless green and purple values may be sacrificed to obtain black.  So a fourth printing in weak black or gray was added, and the three-color became the four-color process.  At the same time, peacock blue was substituted to a large extent for Prussian blue.&nbsp;... While process yellow may be considered lemon yellow, process red, carmine lake, three-color process blue, Prussian blue, and four-color process blue, peacock blue, many variations are encountered in practice;&nbsp;... Bright reds may be mixed from process red and vermilion, chrome greens from process blue and process yellow, and useful purples from process red and reflex blue.}}
</ref><ref name=raymer>
{{cite book | last1=Raymer | first1=Percy C. | title=Photo-engravers' Hand-book on Etching & Finishing |date=1921 |publisher=Effingham Republican |page=52 |url=https://books.google.com/books?id=R8B_pwhP9tgC&pg=PA73 |access-date=6 June 2021 | quote = The so-called pure 'primary red pigment' (more correctly 'magenta') printed onto white paper absorbs the green light (its complementary) and the pure 'blue primary pigment', which is practically a strong cyan or peacock blue, absorbs the bright orange-red light (its complementary).
}}
</ref><ref name=draftsman>
{{cite book | author=United States Bureau of Naval Personnel | title=Illustrator Draftsman 1 & C | date=1967 | publisher=U.S. GPO | page=82 | url = https://books.google.com/books?id=PzlVzeq0VCUC&pg=PA82 |access-date=6 June 2021 | quote = This is based on the fact that most colors can be approximated from a mixture of the primary colors – red, yellow, and blue. However, in process colors, the red is closer to a magenta than a vermilion, the blue is rather pale and greenish, and only the yellow is the bright, clear shade we usually think of as a primary color.}}
</ref> 
Printers traditionally used inks of such colors, known as "process blue" and "process red", before modern color science and the printing industry converged on the process colors (and names) cyan and magenta<ref name=stjohn/><ref name=draftsman/> RYB is not the same as CMY, nor exactly subtractive, but that there is a range of ways to conceptualize traditional RYB as a subtractive system in the framework of modern color science.

Faber-Castell identifies the following three colors: "Cadmium yellow" (number 107) for yellow, "Phthalo blue" (number 110) for blue and "Deep scarlet red" (number 219) for red, as the closest to primary colors for its Art & Graphic color pencils range. "Cadmium yellow" (number 107) for yellow, "Phthalo blue" (number 110) for blue and "Pale geranium lake" (number 121) for red, are provided as primary colors in its basic 5 color "Albrecht Dürer" watercolor marker set.

=== Mixing pigments in limited palettes ===
{{main|Paint mixing}}
[[File:Självporträtt av Anders Zorn 1896.jpg|thumb|upright|An 1896 self-portrait by [[Anders Zorn]] clearly showing a four-pigment palette of what are thought to be white, [[yellow ochre]], [[vermillion]], and black pigments<ref>{{cite book |last1=Harrison |first1=Birge |title=Landscape Painting |date=1909 |publisher=Scribbner |page=118 |url=https://books.google.com/books?id=bCdNRQ20kTYC |language=en |quote=The expert cannot be bothered with useless pigments. He selects the few that are really essential and throws aside the rest as useless lumber. The distinguished Swedish artist, Zorn, uses but two colors—vermilion and yellow ochre; his two other pigments black and white, being the negation of color. With this palette, simple to the point of poverty, he nevertheless finds it possible to paint an immense variety of landscape and figure subjects.}}</ref>]]

The first known use of red, yellow, and blue as "simple" or "primary" colors, by [[Chalcidius]], ca. AD 300, was possibly based on the art of paint mixing.<ref>Kuehni, Rolf G. "Development of the idea of simple colors in the 16th and early 17th centuries". ''Color Research & Application'' 32.2 (2007): 92–99.</ref>

Mixing pigments for the purpose of creating realistic paintings with diverse color gamuts is known to have been practiced at least since [[Ancient Greece]] (see [[#History|history section]]). The identity of a set of minimal pigments to mix diverse gamuts has long been the subject of speculation by theorists whose claims have changed over time, for example, Pliny's white, black, one or another red, and "sil", which might have been yellow or blue; Robert Boyle's white, black, red, yellow, and blue; and variations with more or fewer "primary" color or pigments. Some writers and artists have found these schemes difficult to reconcile with the actual practice of painting.<ref name=gage_apelles>{{cite book |last1=Gage |first1=John |title=Color and Culture: Practice and Meaning from Antiquity to Abstraction |year=1999 |publisher=University of California Press |isbn=978-0-520-22225-0 |url=https://books.google.com/books?id=oq_GtjmoTNgC&q=color+and+culture&pg=PA7 |language=en}}</ref>{{rp|29–38}} Nonetheless, it has long been known that limited palettes consisting of a small set of pigments are sufficient to mix a diverse gamut of colors.<ref name="Boyle1664">{{cite book |last1=Boyle |first1=Robert |date=1664 | publisher=Henry Herringman|title=Experiments and Considerations touching Colours |page=220 |url=http://www.gutenberg.org/ebooks/14504 |quote=But I think I may easily be excus'd (though I do not altogether pass it by) if I restrain my self to the making of a Transient mention of some few of their Practices about this matter; and that only so far forth, as may warrant me to observe to you, that there are but few Simple and Primary Colours (if I may so call them) from whose Various Compositions all the rest do as it were Result. For though Painters can imitate the Hues (though not always the Splendor) of those almost Numberless differing Colours that are to be met with in the Works of Nature, and of Art, I have not yet found, that to exhibit this strange Variety they need imploy any more than White, and Black, and Red, and Blew, and Yellow; these five, Variously Compounded, and (if I may so speak) Decompounded, being sufficient to exhibit a Variety and Number of Colours, such, as those that are altogether Strangers to the Painters Pallets, can hardly imagine.}}</ref><ref>{{cite book |last1=Rood |first1=Ogden |title=Modern chromatics; students' text-book of color, with applications to art and industry. |date=1973 |publisher=Van Nostrand Reinhold Co |location=New York |isbn=0-442-27028-3 |page=108|url=http://lcweb2.loc.gov/service/gdc/scd0001/2010/20100701001mo//20100701001mo.pdf |archive-url=https://web.archive.org/web/20170118111614/http://lcweb2.loc.gov/service/gdc/scd0001/2010/20100701001mo/20100701001mo.pdf |archive-date=2017-01-18 |url-status=live |quote=It is well known to painters that approximate representations of all colours can be produced by the use of very few pigments. Three pigments or coloured powders will suffice, a red, yellow, and a blue; for example, crimson lake, gamboge, and Prussian blue. The red and yellow mingled in various proportions will furnish different shades of orange and orange-yellow; the blue and yellow will give a great variety of greens; the red and blue all the purple and violet hues. There have been instances of painters in water-colours who used only these three pigments, adding lampblack for the purpose of darkening them and obtaining the browns and greys.}}</ref><ref>{{cite journal
| last1   = Nyholm
| first1  = Arvid
| title   = Anders Zorn: The Artist and the Man
| journal = Fine Arts Journal
| date    = 1914
| volume  = 31
| issue   = 4
| pages   = 469–481
| doi     = 10.2307/25587278
| jstor   = 25587278
| quote   = It is true that Zorn uses only a very limited palette, especially when he paints indoors, when he considers that black, white, red and yellow should be enough for all ordinary purposes, except when a very decided color is present, as, for instance, a light blue or a positive green in a drapery.
}}</ref><ref>{{cite book |last1=Munsell |first1=Albert H. |title=A Color Notation |date=1907 |url=http://www.gutenberg.org/files/26054/26054-h/26054-h.htm |quote=Studio and school-room practice still cling to the discredited theory, claiming that, if it fails to describe our color sensations, yet it may be called practically true of pigments, because a red, yellow, and blue pigment suffice to imitate most natural colors.}}</ref><ref>{{cite book |last1=Lintott |first1=E. Barnard |title=The Art of Water Colour Painting |date=1926 |publisher=C. Scribner's Sons |page=25 |url=https://books.google.com/books?id=ycNNAAAAYAAJ |language=en |quote=For a young student there cannot be a better way of entering upon the study of water colour than by rigorously banishing all but two colours from his palette. It is the best and surest way to the study of full colour. The colours should be a cold and warm one; cobalt blue and warm sienna—or Prussian blue and burnt sienna—are two combinations which lend themselves to a great variety of treatment.}}</ref>

The set of pigments available to mix diverse gamuts of color (in various media such as [[oil paint|oil]], [[watercolor painting|watercolor]], [[acrylic paint|acrylic]], [[gouache]], and [[pastel]]) is large and has changed throughout history.<ref>{{cite book |last1=Eastaugh |first1=Nicholas |last2=Walsh |first2=Valentine |last3=Chaplin |first3=Tracey |last4=Siddall |first4=Ruth |title=Pigment Compendium: A Dictionary of Historical Pigments |date=30 March 2007 |publisher=Routledge |isbn=978-1-136-37386-2 |language=en}}</ref><ref>{{cite book |last1=Ball |first1=Philip |title=Bright earth: art and the invention of color |year=2002 |orig-date=2001 |publisher=Farrar, Straus and Giroux |location=New York |isbn=0-226-03628-6 |edition=1st American}}</ref> There is no consensus on a specific set of pigments that are considered primary colors{{snd}} the choice of pigments depends entirely on the artist's subjective preference of subject and style of art, as well as material considerations like [[lightfastness]] and mixing behavior.<ref>{{cite web |last1=MacEvoy |first1=Bruce |title=handprint: learning color through paints |url=https://www.handprint.com/HP/WCL/intstud.html |website=www.handprint.com |access-date=27 April 2021}}</ref> A variety of limited palettes have been employed by artists for their work.<ref>{{cite web |last1=MacEvoy |first1=Bruce |title=palette paintings |url=https://www.handprint.com/HP/WCL/paletfs.html |website=www.handprint.com |access-date=3 February 2021}}</ref><ref>{{cite book |last1=Gurney |first1=James |title=Color and Light: A Guide for the Realist Painter |date=2010 |publisher=Andrews McMeel Publishing |location=Kansas City, Missouri |isbn=978-0-7407-9771-2 |page=104 |url=https://books.google.com/books?id=MvddjqkQy9UC&q=%22limited%20palette%22 |language=en}}</ref>

The color of light (i.e., the spectral power distribution) reflected from illuminated surfaces coated in paint mixes is not well approximated by a subtractive or additive mixing model.<ref>{{cite journal |last1=Haase |first1=Chet S. |last2=Meyer |first2=Gary W. |title=Modeling pigmented materials for realistic image synthesis |journal=ACM Transactions on Graphics |date=1 October 1992 |volume=11 |issue=4 |pages=305–335 |doi=10.1145/146443.146452 |s2cid=6890110 |quote=Section 2 develops some of the significant differences in additive and subtractive color mixing and discusses the need for different mixing theory for pigmented materials.|doi-access=free }}</ref> Color predictions that incorporate light scattering effects of pigment particles and paint layer thickness require approaches based on the [[Kubelka–Munk theory|Kubelka–Munk equations]],<ref>{{cite book |last1=Lu |first1=Jingwan |last2=DiVerdi |first2=Stephen |last3=Chen |first3=Willa A. |last4=Barnes |first4=Connelly |last5=Finkelstein |first5=Adam |title=Proceedings of the Workshop on Non-Photorealistic Animation and Rendering |chapter=RealPigment: Paint compositing by example |date=8 August 2014 |pages=21–30 |doi=10.1145/2630397.2630401|isbn=978-1-4503-3020-6 |s2cid=1415118 }}</ref> but even such approaches are not expected to predict the color of paint mixtures precisely due to inherent limitations.<ref>{{cite book |last1=Curtis |first1=Cassidy J. |last2=Anderson |first2=Sean E. |last3=Seims |first3=Joshua E. |last4=Fleischer |first4=Kurt W. |last5=Salesin |first5=David H. |title=Proceedings of the 24th annual conference on Computer graphics and interactive techniques - SIGGRAPH '97 |chapter=Computer-generated watercolor |date=1997 |pages=421–430 |doi=10.1145/258734.258896 |isbn=0-89791-896-7 |s2cid=3051452 |quote=In summary, the fact that the KM model appears to work so well could actually be considered quite surprising, given the number of basic assumptions of the model violated by watercolor. We suspect that while the results of the model are probably not very physically accurate, they at least provide very plausible physical approximations, which appear quite adequate for many applications.}}</ref> Artists typically rely on mixing experience and "recipes"<ref>{{cite book |last1=Powell |first1=William F. |title=1,500 Color Mixing Recipes for Oil, Acrylic & Watercolor: Achieve Precise Color when Painting Landscapes, Portraits, Still Lifes, and More |date=August 2012 |publisher=Walter Foster Publishing |isbn=978-1-60058-283-7 |url=https://books.google.com/books?id=RsGJFZs5yyIC |language=en}}</ref><ref>{{cite web |last1=MacEvoy |first1=Bruce |title=handprint: basic mixing method |url=https://www.handprint.com/HP/WCL/mix.html |website=www.handprint.com}}</ref> to mix desired colors from a small initial set of primaries and do not use mathematical modeling.

MacEvoy explains why artists often chose a palette closer to RYB than to CMY:<ref>{{cite web |last1=MacEvoy |first1=Bruce |title=imaginary or imperfect primaries |url=http://www.handprint.com/HP/WCL/color6.html#imaginary |website=handprint.com |access-date=13 June 2021}}</ref>{{unreliable source?|date=December 2024}} 
{{blockquote
|text=Because the 'optimal' pigments in practice produce unsatisfactory mixtures; because the alternative selections are less granulating, more transparent, and mix darker values; and because visual preferences have demanded relatively saturated yellow to red mixtures, obtained at the expense of relatively dull green and purple mixtures. Artists jettisoned 'theory' to obtain the best color mixtures in practice.}}
{{clear}}

== Color space primaries ==
[[File:Colormatch.svg|thumb|A conceptual visualization of a color matching experiment. A circular foveal bipartite field (about the size one's thumbnail an arm's length away<ref>{{cite web |title=What is Meant by the Term "Observer Angle"? |url=https://www.xrite.com/service-support/what_is_meant_by_the_term_observer_angle |website=X-Rite |access-date=12 May 2021 |language=en}}</ref>) is presented to the observer in a dark surround. One part of the field is illuminated by a monochromatic test stimulus. The participant adjusts the intensities of the three coincident monochromatic primary lights (which are usually red, green and blue hues) on either field until both the test stimulus and match stimulus appear as the exact same color. In this case the participant has added red to the 480 nm test stimulus and has almost matched the match stimulus made of only the green and blue lights of comparable intensities. The specific monochromatic primaries shown here are from the Stiles-Burch 1955 experiment.<ref>{{cite journal |last1=Stiles |first1=W.S. |last2=Burch |first2=J. M. |title=Interim Report to the Commission Internationale de l'Eclairage, Zurich, 1955, on the National Physical Laboratory's Investigation of Colour-matching (1955) |journal=Optica Acta: International Journal of Optics |date=December 1955 |volume=2 |issue=4 |pages=168–181 |doi=10.1080/713821039|bibcode=1955AcOpt...2..168S }}</ref>]]

[[File:Canonical color matching functions.png|thumb|The [[CIE RGB]],<ref>{{cite journal |last1=Stiles |first1=W.S. |last2=Burch |first2=J. M. |title=Interim Report to the Commission Internationale de l'Eclairage, Zurich, 1955, on the National Physical Laboratory's Investigation of Colour-matching (1955) |journal=Optica Acta: International Journal of Optics |date=December 1955 |volume=2 |issue=4 |pages=168–181 |doi=10.1080/713821039|bibcode=1955AcOpt...2..168S }}</ref><ref>{{cite web |title=Colour matching functions - Stiles & Burch (1955) 2-deg, RGB CMFs |url=http://cvrl.ioo.ucl.ac.uk/cmfs.htm |website=cvrl.ioo.ucl.ac.uk}}</ref> [[CIE XYZ]]<ref>{{cite web |title=Colour matching functions - 2-deg XYZ CMFs transformed from the CIE (2006) 2-deg LMS cone fundamentals |url=http://cvrl.ioo.ucl.ac.uk/cmfs.htm |website=cvrl.ioo.ucl.ac.uk}}</ref> color matching functions and [[LMS color space|LMS]] cone fundamentals.<ref>{{cite book |title=Fundamental chromaticity diagram with physiological axes. Part 1. |date=2006 |publisher=Commission internationale de l'eclairage |location=Vienna, Austria |isbn=978-3-901906-46-6}}</ref><ref>{{cite web |title=CVRL functions - 2-deg fundamentals based on the Stiles and Burch 10-deg CMFs adjusted to 2-deg |url=http://www.cvrl.org/cvrlfunctions.htm |website=www.cvrl.org}}</ref> The curves are all for 2° fields.]]
A [[color space]] is a subset of a [[color model]], where the primaries have been defined, either directly as photometric spectra, or indirectly as a function of other color spaces. For example, [[sRGB]] and [[Adobe RGB]] are both color spaces based on the [[RGB color model]]. However, the green primary of Adobe RGB is more saturated than the equivalent in sRGB, and therefore yields a larger [[gamut]].<ref name="sRGBVsAdobeRGB">{{cite web|url=https://www.cambridgeincolour.com/tutorials/sRGB-AdobeRGB1998.htm|title=sRGB vs. Adobe RGB 1998|website=Cambridge in Colour}}</ref> Otherwise, choice of color space is largely arbitrary and depends on the utility to a specific application.<ref name="handprintprimaries"/>

=== Imaginary primaries ===
Color space primaries are derived from canonical colorimetric experiments that represent a standardized model of an observer (i.e., a set of ''color matching functions'') adopted by [[International Commission on Illumination|Commission Internationale de l'Eclairage]] (CIE) standards. The abbreviated account of color space primaries in this section is based on descriptions in ''Colorimetry - Understanding The CIE System''.<ref name="Schanda2007">{{cite book |editor1-last=Schanda |editor1-first=János |title=Colorimetry: understanding the CIE system |date=2007 |publisher=CIE/Commission internationale de l'eclairage |location=[Vienna, Austria] |isbn=978-0-470-04904-4}}</ref>

The [[CIE 1931]] standard observer is derived from experiments in which participants observe a foveal secondary bipartite [[field of view|field]] with a dark surround. Half of the field is illuminated with a monochromatic ''test stimulus'' (ranging from 380&nbsp;nm to 780&nbsp;nm) and the other half is the ''matching stimulus'' illuminated with three coincident monochromatic primary lights: 700&nbsp;nm for red (R), 546.1&nbsp;nm for green (G), and 435.8&nbsp;nm for blue (B).<ref name="Schanda2007"/>{{rp|29}} These primaries correspond to [[CIE RGB|CIE RGB color space]]. The intensities of the primary lights could be adjusted by the participant observer until the matching stimulus matched the test stimulus, as predicted by Grassman's laws of additive mixing. Different standard observers from other color matching experiments have been derived since 1931. The variations in experiments include choices of primary lights, field of view, number of participants etc.<ref>{{cite journal |last1=Li |first1=Jiaye |last2=Hanselaer |first2=Peter |last3=Smet |first3=Kevin A. G. |title=Impact of Color-Matching Primaries on Observer Matching: Part I – Accuracy |journal=LEUKOS |date=17 February 2021 |volume=18 |issue=2 |pages=104–126 |doi=10.1080/15502724.2020.1864395|doi-access=free }}</ref> but the presentation below is representative of those results.

Matching was performed across many participants in incremental steps along the range of test stimulus wavelengths (380&nbsp;nm to 780&nbsp;nm) to ultimately yield the color matching functions: <math>\overline{r}(\lambda)</math>, <math>\overline{g}(\lambda)</math> and <math>\overline{b}(\lambda)</math> that represent the relative intensities of red, green, and blue light to match each wavelength (<math>\lambda</math>). These functions imply that <math>[C]</math> units of the test stimulus with ''any'' spectral power distribution, <math>P(\lambda)</math>, can be matched by {{math|[R]}}, {{math|[G]}}, and {{math|[B]}} units of each primary where:<ref name="Schanda2007"/>{{rp|28}}

{{NumBlk|:|<math>
[C] =
\int_{380\text{ nm}}^{780\text{ nm}} \overline{r}(\lambda) P(\lambda)\,d\lambda \cdot [R] +
\int_{380\text{ nm}}^{780\text{ nm}} \overline{g}(\lambda) P(\lambda)\,d\lambda \cdot [G] +
\int_{380\text{ nm}}^{780\text{ nm}} \overline{b}(\lambda) P(\lambda)\,d\lambda \cdot [B].
</math>|{{EquationRef|Eq. 1}}}}

Each integral term in the above equation is known as a ''tristimulus value'' and measures amounts in the adopted units. No set of real primary lights can match another monochromatic light under additive mixing so at least one of the color matching functions is negative for each wavelength. A negative tristimulus value corresponds to that primary being added to the test stimulus instead of the matching stimulus to achieve a match.

The negative tristimulus values made certain types of calculations difficult, so the CIE put forth new color matching functions <math>\overline{x}(\lambda)</math>, <math>\overline{y}(\lambda)</math>, and <math>\overline{z}(\lambda)</math> defined by the following [[linear map|linear transformation]]:<ref name="Schanda2007"/>{{rp|30}}

{{NumBlk|:|<math>
\begin{bmatrix}
 \overline{x}(\lambda) \\
 \overline{y}(\lambda) \\
 \overline{z}(\lambda)
\end{bmatrix}
=
\begin{bmatrix}
 2.768892 & 1.751748 & 1.130160 \\
 1.000000 & 4.590700 & 0.060100 \\
 0 & 0.056508 & 5.594292 \\
\end{bmatrix}
\begin{bmatrix}
 \overline{r}(\lambda) \\
 \overline{g}(\lambda) \\
 \overline{b}(\lambda)
\end{bmatrix}.
</math>|{{EquationRef|Eq. 2}}}}

These new color matching functions correspond to ''imaginary'' primary lights X, Y, and Z ([[CIE XYZ|CIE XYZ color space]]). All colors can be matched by finding the amounts {{math|[X]}}, {{math|[Y]}}, and {{math|[Z]}} analogously to {{math|[R]}}, {{math|[G]}}, and {{math|[B]}} as defined in {{EquationNote|Eq. 1}}. The functions <math>\overline{x}(\lambda)</math>, <math>\overline{y}(\lambda)</math>, and <math>\overline{z}(\lambda)</math> based on the specifications that they should be nonnegative for all wavelengths, <math>\overline{y}(\lambda)</math> be equal to [[luminous efficiency function|photometric luminance]], and that <math>[X]=[Y]=[Z]</math> for an equienergy (i.e., a uniform spectral power distribution) test stimulus.<ref name="Schanda2007"/>{{rp|30}}

Derivations use the color matching functions, along with data from other experiments, to ultimately yield the ''cone fundamentals'': <math>\overline{l}(\lambda)</math>, <math>\overline{m}(\lambda)</math> and <math>\overline{s}(\lambda)</math>. These functions correspond to the response curves for the three types of color [[photoreceptor cell|photoreceptors]] found in the human retina: long-wavelength (L), medium-wavelength (M), and short-wavelength (S) [[cone cell|cones]]. The three cone fundamentals are related to the original color matching functions by the following linear transformation (specific to a 10° field):<ref name="Schanda2007"/>{{rp|227}}
 
{{NumBlk|:|<math>
\begin{bmatrix}
 \overline{l}(\lambda) \\
 \overline{m}(\lambda) \\
 \overline{s}(\lambda)
\end{bmatrix}
=
\begin{bmatrix}
 0.192325269 & 0.749548882 & 0.0675726702 \\
 0.0192290085 & 0.949098496 & 0.113830196 \\
 0 & 0.0105107859 & 0.991427669 \\
\end{bmatrix}
\begin{bmatrix}
 \overline{r}(\lambda) \\
 \overline{g}(\lambda) \\
 \overline{b}(\lambda)
\end{bmatrix}.
</math>|{{EquationRef|Eq. 3}}}}

[[LMS color space]] comprises three primary lights (L, M, and S) that stimulate only the L-, M-, and S-cones respectively. A real primary that stimulates only the M-cone is impossible, and therefore these primaries are imaginary. The [[LMS color space]] has significant physiological relevance as these three photoreceptors mediate trichromatic color vision in humans.

Both XYZ and LMS color spaces are ''complete'' since all colors in the gamut of the standard observer are contained within their color spaces. Complete color spaces must have imaginary primaries, but color spaces with imaginary primaries are not necessarily complete (e.g. [[ProPhoto RGB color space]]).

=== Real primaries ===
[[File:CIE1931xy_gamut_comparison.svg |thumb|300px|Various RGB color spaces are represented as [[color triangle]]s with vertices that represent the primaries. The [[CIE 1931 color space|1931 CIE chromaticity diagram]] shows the gamut of the standard observer. Primaries outside of the colored region are imaginary.]]

Color spaces used in [[color reproduction]] must use real primaries that can be reproduced by practical sources, either lights in additive models, or pigments in subtractive models. Most [[RGB color spaces]] have real primaries, though some maintain imaginary primaries. For example, all the [[sRGB]] primaries fall within the gamut of human perception, and so can be easily represented by practical light sources, including CRT and LED displays, hence why sRGB is still the color space of choice for digital displays.

A color in a color space is defined as a combination of its primaries, where each primary must give a non-negative contribution. Any color space based on a finite number of real primaries is ''incomplete'' in that it cannot reproduce every color within the gamut of the standard observer.

Practical color spaces such as [[sRGB]]<ref name="sRGB_orig">{{cite web|author1=Michael Stokes|author2=Matthew Anderson|author3=Srinivasan Chandrasekar|author4=Ricardo Motta|date=5 November 1996|title=A Standard Default Color Space for the Internet – sRGB, Version 1.10|url=https://www.w3.org/Graphics/Color/sRGB.html <!-- ALTERNATIVE URL: http://www.color.org/sRGB.xalter -->|website=}}</ref> and [[scRGB]]<ref name="iec-standard">{{Cite web|url=https://webstore.iec.ch/publication/6171|title=Multimedia systems and equipment - Colour measurement and management - Part 2-2: Colour management - Extended RGB colour space - scRGB|date=23 January 2003|access-date=18 April 2021|author1=HP|author-link1=Hewlett-Packard|author2=Microsoft|author-link2=Microsoft|author3=IEC|author-link3=International Electrotechnical Commission|editor=IEC|website=IEC}}</ref> are typically (at least partially) defined in terms of linear transformations from CIE XYZ, and [[color management]] often uses CIE XYZ as a middle point for transformations between two other color spaces.

Most color spaces in the color-matching context (those defined by their relationship to CIE XYZ) inherit its three-dimensionality. However, more complex [[color appearance model]]s like [[CIECAM02]] require extra dimensions to describe colors appear under different viewing conditions.<ref>{{cite book |last1=Fairchild |first1=Mark D. |title=Color Appearance Models. |date=2013 |publisher=Wiley |location=Hoboken |isbn=978-1-119-96703-3 |page=287 |edition=3rd}}</ref>

{{clear}}

== Psychological primaries ==
[[File:Hering Color Cricles.png|thumb|upright=1.0|[[Ewald Hering]]'s illustration<ref>{{cite book |last1=Hering |first1=Ewald |title=Grundzüge der Lehre vom Lichtsinn |year=1920 |publisher=Springer Berlin Heidelberg |isbn=978-3-662-42174-1 |url=https://books.google.com/books?id=M1xVAAAAMAAJ |language=de}}</ref> of the psychological primaries. Red/green and yellow/blue form opponent pairs (top). Each color can be psychologically mixed to make other colors (bottom) with both members of the other pair but not with its opponent according to Hering.]]
{{Main|Unique hues}}

The [[opponent process]] was proposed by [[Ewald Hering]] in which he described the four [[unique hues]] (later called psychological primaries in some contexts): red, green, yellow and blue.<ref>{{cite book |last1=Hering |first1=Ewald |title=Outlines of a theory of the light sense. |date=1964 |publisher=Harvard Univ. Press |language=English}}</ref> To Hering, the unique hues appeared as pure colors, while all others were "psychological mixes" of two of them. Furthermore, these colors were organized in "opponent" pairs, red vs. green and yellow vs. blue so that mixing could occur across pairs (e.g., a yellowish green or a yellowish red) but not within a pair (i.e., [[reddish green]] cannot be imagined). An achromatic opponent process along black and white is also part of Hering's explanation of color perception. Hering asserted that we did not know why these color relationships were true but knew that they were.<ref>{{cite book |last1=Turner |first1=R. Steven |title=In the eye's mind: vision and the Helmholtz-Hering controversy |date=1994 |publisher=Princeton University Press |location=Princeton, New Jersey |isbn=978-1-4008-6381-5 |pages=130–133 |language=en}}</ref> Although there is a great deal of evidence for the opponent process in the form of neural mechanisms,<ref>{{cite journal
| last1   = Conway
| first1  = Bevil R.
| title   = Color Vision, Cones, and Color-Coding in the Cortex
| journal = The Neuroscientist
| date    = 12 May 2009
| volume  = 15
| issue   = 3
| pages   = 274–290
| doi     = 10.1177/1073858408331369
| pmid = 19436076
| s2cid = 9873100
}}</ref> there is currently no clear mapping of the psychological primaries to [[neural correlate]]s.<ref>{{cite book |last1=MacLeod |first1=Donald |editor1-last=Cohen |editor1-first=Jonathan |editor2-last=Matthen |editor2-first=Mohan |title=Color Ontology and Color Science |date=21 May 2010 |publisher=MIT Press |isbn=978-0-262-01385-7 |pages=159–162 |url=https://books.google.com/books?id=-SYTDgAAQBAJ&q=Into+the+Neural+Maze.+In%3A+Color+Ontology+and+Color+Science.&pg=PA151 |language=en|quote="Many color scientists, acknowledging that the color opponent signals observed in the pathway to cortex have no relation to the psychological primaries, do nevertheless take it for granted that a color opponent neural representation capable of accounting for the phenomenally simple or unitary quality of the psychological primaries must exist somewhere in the brain—in a region that is directly reflected in phenomenal experience, instead of merely conveying signals from the eye. This tenet was long maintained in the absence of neurophysiological evidence, and continues to be maintained even though current neurophysiological evidence does not support it."}}</ref>

The psychological primaries were applied by [[Richard S. Hunter]] as the primaries for [[Hunter Lab|Hunter L,a,b]] colorspace that led to the creation of [[CIELAB color space|CIELAB]].<ref>{{cite web |title=Application Note AN 1005.00 Measuring color using Hunter L, a, b versus CIE 1976 L*a*b* |url=https://www.hunterlab.com/media/documents/duplicate-of-an-1005-hunterlab-vs-cie-lab.pdf |archive-url=https://web.archive.org/web/20210829054654/https://www.hunterlab.com/media/documents/duplicate-of-an-1005-hunterlab-vs-cie-lab.pdf |archive-date=2021-08-29 |url-status=live |website=HunterLab |publisher=Hunter Associates Laboratory Inc |access-date=10 March 2021 |quote=Hunter L, a, b and CIE 1976 L*a*b* (CIELAB) are both color scales based on the Opponent-Color Theory.}}</ref> The [[Natural Color System]] is also directly inspired by the psychological primaries.<ref>{{cite book
| last1     = Maffi
| first1    = Luisa
| editor-last1 = Hardin
| editor-first1 = C.L.
| title     = Color categories in thought and language
| date      = 1997
| publisher = Cambridge University Press
| location  = Cambridge
| isbn      = 978-0-521-49800-5
| pages     = 163–192
| edition   = 1. publ.
| url       = https://books.google.com/books?id=ix8l5X5ZBogC&q=%22natural+color+system%22&pg=PA163
}}</ref>

== History ==

=== Philosophy ===
Philosophical writing from ancient Greece has described notions of primary colors, but they can be difficult to interpret in terms of modern color science. [[Theophrastus]] (c. 371–287 BCE) described [[Democritus]]' position that the primary colors were white, black, red, and green.<ref name="renzoshamey2020">{{cite book |last1=Shamey |first1=Renzo |last2=Kuehni |first2=Rolf G. |title=Pioneers of Color Science |date=2020 |doi=10.1007/978-3-319-30811-1|isbn=978-3-319-30809-8 |s2cid=241801540 }}</ref>{{rp|4}} In [[Classical Greece]], [[Empedocles]] identified white, black, red, and, (depending on the interpretation) either yellow or green as primary colors.<ref name="renzoshamey2020"/>{{rp|8}} [[Aristotle]] described a notion in which white and black could be mixed in different ratios to yield chromatic colors;<ref name="renzoshamey2020"/>{{rp|12}} this idea had considerable influence in Western thinking about color. [[François d'Aguilon]]'s 16th century notion of the five primary colors (white, yellow, red, blue, black) was influenced by Aristotle's idea of the chromatic colors being made of black and white.<ref name="renzoshamey2020"/>{{rp|87}}The 20th century philosopher [[Ludwig Wittgenstein]] explored color-related ideas using red, green, blue, and yellow as primary colors.<ref>{{cite journal
 |last1        = Beran
 |first1       = Ondrej
 |title        = The Essence (?) of Color, According to Wittgenstein
 |journal      = From the ALWS Archives: A Selection of Papers from the International Wittgenstein Symposia in Kirchberg Am Wechsel
 |date         = 2014
 |url          = http://wittgensteinrepository.org/agora-alws/article/view/2704/3132
 |access-date  = 2017-12-11
 |archive-date = 2017-12-11
 |archive-url  = https://web.archive.org/web/20171211104829/http://wittgensteinrepository.org/agora-alws/article/view/2704/3132
 }}</ref><ref>{{cite book |last1=Wittgenstein |first1=Ludwig |title=The Big Typescript, TS. 213 |date=2005 |publisher=Blackwell Pub |location=Malden, MA |isbn=978-1-4051-0699-3 |edition=German-English scholar's}}</ref>
[[File:Franciscus Aguilonius color scheme.png|thumb|upright=1.4|The color scheme of [[François d'Aguilon]], where the two simple colors of white (albus) and black (niger) are mixed to the "noble" colors of yellow (flavus), red (rubeus), and blue (caeruleus). Orange (aureus), purple (purpureus), and green (viridis) are each combinations of two noble colors.<ref>{{cite web |last1=MacEvoy |first1=Bruce |title= do "primary" colors exist?|url=https://www.handprint.com/HP/WCL/color6.html |website=handprint : colormaking attributes|access-date=1 December 2020 |quote=From a modern perspective, the most peculiar feature of d'Aguilon's theory is that these three "noble" hues were themselves created from the mysterious blending of white and black, or light and dark (upper curved lines in the figure), so that light and dark were the two "simple" or primary colors. The "composite" hues green, orange (gold), and purple (lower curved lines) were mixed from the "noble" triad colors. D'Aguilon's diagram was reprinted by the Jesuit scholar Athanasius Kircher in his optical treatise Ars magna lucis et umbrae (The Great Art of Light and Shadow, 1646). Both sources were widely read in the 17th century, and shaped the explanation of color mixing dominant during the Baroque.}}</ref>]]

=== Light and color vision ===

[[Isaac Newton]] used the term "primary color" to describe the colored spectral components of sunlight.<ref>{{Cite book|url=https://www.gutenberg.org/files/33504/33504-h/33504-h.htm|title=Opticks: Or, A Treatise of the Reflections, Refractions, Inflections and Colours of Light|last=Newton|first=Isaac|date=1730|publisher=William Innys at the West-End of St. Paul's.|language=en|page=135 |quote="Whiteness and all grey Colours between white and black, may be compounded of Colours, and the whiteness of the Sun's Light is compounded of all the primary Colours mix'd in a due Proportion"}}</ref><ref>{{cite journal |last1=Newton |first1=Isaac |title=A Letter of Mr. Isaac Newton … containing his New Theory about Light and Color |journal=Philosophical Transactions of the Royal Society |date=19 February 1671 |issue=80 |pages=3075–3087 |url=http://www.newtonproject.ox.ac.uk/view/texts/normalized/NATP00006 |access-date=19 November 2020 |quote=The Original or primary colours are, Red, Yellow, Green, Blew, and a Violet-purple, together with Orange, Indico, and an indefinite variety of Intermediate gradations. |archive-date=15 February 2022 |archive-url=https://web.archive.org/web/20220215225401/https://www.newtonproject.ox.ac.uk/view/texts/normalized/NATP00006 }}</ref> A number of color theorists did not agree with Newton's work. [[David Brewster]] advocated that red, yellow, and blue light could be combined into any spectral hue late into the 1840s.<ref>{{cite web |last1=Boker |first1=Steven M. |title=The Representation of Color Metrics and Mappings in Perceptual Color Space |url=http://people.virginia.edu/~smb3u/ColorVision2/node6.html |website=The Representation of Color Metrics and Mappings in Perceptual Color Space}}</ref><ref>{{cite web |last1=MacEvoy |first1=Bruce |title=handprint: colormaking attributes |url=https://www.handprint.com/HP/WCL/color6.html |website=www.handprint.com |quote=The Scottish physicist David Brewster (1781-1868) was an especially pugnacious holdout, arguing as late as the 1840's that all spectral hues could be explained by red, yellow, and blue fundamental colors of light, which Brewster equated with three colored filters or transmittance curves that could reproduce the entire spectrum...}}</ref> [[Thomas Young (scientist)|Thomas Young]] proposed red, green, and violet as the three primary colors, while [[James Clerk Maxwell]] favored changing violet to blue.<ref>{{cite book |last1=Maxwell |first1=James Clerk |title=The Scientific Papers of James Clerk Maxwell |publisher=Courier Corporation |year=2013|isbn=978-0-486-78322-2 |url=https://books.google.com/books?id=EA7CAgAAQBAJ&pg=PA449 |language=en |page=49 |quote=The experiments with pigments do not indicate what colours are to be considered as primary; but experiments on the prismatic spectrum shew that all the colours of the spectrum, and therefore all the colours in nature, are equivalent to mixtures of three colours of the spectrum itself, namely, red, green (near the line E), and blue (near the line G). Yellow was found to be a mixture of red and green.}}</ref> [[Hermann von Helmholtz]] proposed "a slightly purplish red, a vegetation-green, slightly yellowish, and an ultramarine-blue" as a trio.<ref>{{cite book
| title     = A text book of the principles of physics
| author    = Alfred Daniell
| publisher = Macmillan and Co
| year      = 1904
| page      = 575
| url       = https://books.google.com/books?id=oPQZAAAAYAAJ&q=primary+red-green-and-violet+maxwell&pg=PA575
}}</ref> Newton, Young, Maxwell, and Helmholtz were all prominent contributors to "modern color science"<ref name="Mollon2003">{{cite book |last1=Mollon |first1=J.D. |title=The science of color |date=2003 |publisher=Elsevier |location=Amsterdam |isbn=0-444-51251-9 |pages=1–39 |citeseerx=10.1.1.583.1688 |edition=2nd }}</ref>{{rp|1–39}} that ultimately described the perception of color in terms of the three types of retinal photoreceptors.

=== Colorants ===
Twentieth century art historian
[[John Gage (art historian)|John Gage]]'s ''The Fortunes Of Apelles'' provides a summary of the history of primary colors<ref name="gage_apelles"/> as pigments in painting and describes the evolution of the idea as complex. Gage begins by describing [[Pliny the Elder]]'s account of notable Greek painters who used four primaries.<ref>{{cite book |title=Pliny the Elder, The Natural History, Book XXXV. An Account of Paintings and Colours. |url=https://www.perseus.tufts.edu/hopper/text?doc=Perseus:abo:phi,0978,001:35 |chapter=32 |quote=It was with four colours only, that Apelles, Echion, Melanthius, and Nicomachus, those most illustrous painters, executed their immortal works; melinum for the white, Attic sil for the yellow, Pontic sinopis for the red, and atramentum for the black; and yet a single picture of theirs has sold before now for the treasures of whole cities. But at the present day, when purple is employed for colouring walls even, and when India sends to us the slime of her rivers, and the corrupt blood of her dragons and her elephants, there is no such thing as a picture of high quality produced. Everything, in fact, was superior at a time when the resources of art were so much fewer than they now are. Yes, so it is; and the reason is, as we have already stated, that it is the material, and not the efforts of genius, that is now the object of research.}}</ref> Pliny distinguished the pigments (i.e., substances) from their apparent colors: white from Milos (''ex albis''), red from Sinope (''ex rubris''), Attic yellow (''sil'') and [[atramentum]] (''ex nigris''). Sil was historically confused as a blue pigment between the 16th and 17th centuries, leading to claims about white, black, red, and blue being the fewest colors required for painting. [[Thomas Bardwell]], an 18th century Norwich portrait painter, was skeptical of the practical relevance of Pliny's account.<ref>{{cite book |last1=Bardwell |first1=Thomas |last2=Richardson |first2=Samuel |last3=Millar |first3=Andrew |last4=Dodsley |first4=Robert |last5=Dodsley |first5=James |last6=Rivington |first6=John |last7=Rivington |first7=James |last8=Vivarès |first8=François |title=The practice of painting and perspective made easy: in which is contained, the art of painting in oil, with the method of colouring ... and a new, short, and familiar account of the art of perspective, illustrated with copper-plates, engraved by Mr. Vivares |year=1756 |publisher=London : Printed by S. Richardson, for the author, and sold by him ... and by A. Millar ... R. and J. Dodsley ..., and J. and J. Rivington ... |url=https://archive.org/details/practiceofpainti00bard/page/n15/mode/2up?q=ancients |quote=How it really was, Time has put it out of our Power to determine : But if we ſuppoſe thoſe four principal Colours in Perfection, then, I think, it can be no longer doubted, but that from them might be made all the various Colours in Nature. For my part, I cannot believe, that the four capital Colours of the Antients would mix to that ſurpriſing Perfection we ſee in the Works of Titian and Rubens. And if we have no certain Knowlege of their Method of Colouring who lived In the laſt Century, how ſhould we underſtand theirs who lived near Two thouſand Years ago ?}}</ref>

[[Robert Boyle]], the Irish chemist, introduced the term ''primary color'' in English in 1664 and claimed that there were five primary colors (white, black, red, yellow, and blue).<ref name="Boyle1664"/><ref>{{cite web |last1=Briggs |first1=David |title=The Dimensions of Colour, primary colours |url=http://www.huevaluechroma.com/062.php |website=www.huevaluechroma.com}}</ref> The German painter [[Joachim von Sandrart]] eventually proposed removing white and black from the primaries and that one only needed red, yellow, blue, and green to paint "the whole creation".<ref name="gage_apelles"/>{{rp|36}}

{| class="wikitable"
|+ Partial list of authors describing red, yellow, and blue as the (chromatic) primary colors before 18th century (adapted from Shamey and Kuehni)<ref name="renzoshamey2020"/>{{rp|108}}
|-
! Year !! Author !! Color terms !! Descriptive term
|-
| c. 325 || [[Chalcidius]] || Pallidus, rubeus, cyaneus || Generic colors
|-
| c. 1266 || [[Roger Bacon]] || Glaucus, rubeus, viriditas || Principal species
|-
| c. 1609 || [[Anselmus de Boodt]] || Flavus, ruber, caeruleus || Principal colors
|-
| c. 1613 || [[François d'Aguilon]] || Flavus, rubeus, caeruleus || Simple colors
|-
| c. 1664 || [[Robert Boyle]] || Yellow, red, blue || Simple, primary
|-
| c. 1680 || [[André Félibien]] || Jaune, rouge, bleu || Principal, primitive
|}

Red, yellow, and blue as primaries became a popular notion in the 18th and 19th centuries. [[Jacob Christoph Le Blon]], an engraver, was the first to use separate plates for each color in [[mezzotint]] [[printmaking]]: yellow, red, and blue, plus black to add shades and contrast. Le Blon used ''primitive'' in 1725 to describe red, yellow, and blue in a very similar sense as Boyle used ''primary''.<ref name="Mollon2003"/>{{rp|6|quote=In 1725, however, he published a slender volume entitled Coloritto, in which he sets out the principle of trichromatic color mixing (Figure 1.4). It is interesting that he gives the same primaries in the same order (yellow, red, and blue) as does the anonymous author of the 1708 text, and uses the same term for them, ''couleurs primitives''}} [[Moses Harris]], an entomologist and engraver, also describes red, yellow, and blue as "primitive" colors in 1766.<ref>{{cite book |last1=Harris |first1=Moses |title=The natural system of colours: wherein is displayed the regular and beautiful order and arrangement, arising from the three premitives, red, blue, and yellow, the manner in which each colour is formed, and its composition, the dependance [sic] they have on each other, and by their harmonious connections are produced the teints, or colours, of every object in the creation, and those teints, tho' so numerous as 660, are all comprised in thirty three terms, only |date=1766 |publisher=Laidler's office, Princes-Street, Licester-Fields |url=https://www.loc.gov/item/50048542/}}</ref> [[Léonor Mérimée]] described red, yellow, and blue in his book on painting (originally published in French in 1830) as the three simple/primitive colors that can make a "great variety" of tones and colors found in nature.<ref>{{cite book |last1=Mérimée |first1=Jean-François-Léonor |last2=Taylor |first2=William Benjamin Sarsfield |title=The Art of Painting in Oil and in Fresco, Being a History of the Various Processes and Materials Employed, from Its Discovery |publisher=Whittaker & co. |year=1839 |page=245 |url=https://archive.org/details/artpaintinginoi01taylgoog/page/n300/mode/2up?q=simple |language=en |quote=Although painters usually have arranged on their palettes a good many pigments of various deno- minations, yet they do not always seem to know, that three simple colours (yellow, red, and blue) can, by proper combination, be made to produce that great variety of tones and colours that we find in nature. United in pairs, these three primitive colours give birth to three other colours, as distinct and as brilliant as their originals; as thus, the yellow, mixed with red, gives the orange; the red and blue, violet; and the green is obtained by mixing blue and yellow, and, according to the preponderance of one or other colour in the mixture, will the tint incline towards that colour; and as these proportions are graduated, we pass progressively from one colour to another, and from whatever point we begin, we return to it.}}</ref> [[George Field (chemist)|George Field]], a chemist, used the word ''primary'' to describe red, yellow, and blue in 1835.<ref>{{cite book |last1=Field |first1=George |title=Chromatography; Or, A Treatise on Colours and Pigments: And of Their Powers in Painting |publisher=Tilt and Bogue |year= 1835 |url=https://books.google.com/books?id=PDMAAAAAQAAJ&q=%22primary+colours%22+yellow+red+blue+%22entire+colours%22&pg=PA38 |language=en |quote=The Primary Colours are such as yield others by being compounded, but are not themselves capable of being produced by composition by other colours. They are three only, yellow, red, and blue...}}</ref> [[Michel Eugène Chevreul]], also a chemist, discussed red, yellow, and blue as "primary" colors in 1839.<ref>{{cite book | author = Chevreul, Michel Eugène | title = The Laws of Contrast of Colour | year = 1861 | publisher = Routledge, Warne, and Routledge | place = London | url = https://archive.org/details/lawscontrastcol00chevgoog| page = [https://archive.org/details/lawscontrastcol00chevgoog/page/n70 25] }} – English translation by John Spanton</ref><ref>{{cite web |last1=MacEvoy |first1=Bruce |title=handprint: colormaking attributes |url=https://www.handprint.com/HP/WCL/chevreul.html |website=www.handprint.com}}</ref>

=== Color order systems ===

[[File:Lambert Farbenpyramide 1772.jpg|thumb|[[Johann Heinrich Lambert]]'s "Farbenpyramide" tetrahedron published in 1772. Gamboge (yellow), carmine (red), and Prussian blue pigments are used the corner swatches of each "level" of lightness with mixtures filling the others and white at the top.<ref name="Lambert1772">{{cite book |last1=Lambert |first1=J.H. |title=Beschreibung einer mit Calauischem Wachse ausgeführten Farbenpyramide |date=1772 |publisher=Haude und Spener |location=Berlin}}</ref>]]

[[File:Runge RYB sketch.png|thumb|[[Philipp Otto Runge]]'s sketch showing bl (blue), g (yellow) and r (red) as the fundamental colors<ref name="Lambert1772" />{{rp|86}}]]

Historical perspectives<ref>{{cite web |last1=MacEvoy |first1=Bruce |title=handprint: colormaking attributes |url=https://www.handprint.com/HP/WCL/color6.html#solidmodels |website=www.handprint.com}}</ref> on color order systems<ref>{{cite book |last1=Kuehni |first1=Rolf G. |title=Color space and its divisions: color order from antiquity to the present |date=2003 |publisher=Wiley-Interscience |location=Hoboken, N.J. |isbn=978-0-471-43226-5}}</ref> ("catalogs" of color) that were proposed in the 18th and 19th centuries describe them as using red, yellow, and blue pigments as chromatic primaries. [[Tobias Mayer]] (a German mathematician, physicist, and astronomer) described a [[triangular bipyramid]] with red, yellow and blue at the 3 vertices in the same plane, white at the top vertex, and black and the bottom vertex in a public lecture in 1758.<ref name="renzoshamey2020"/>{{rp|115}} There are 11 planes of colors between the white and black vertices inside the triangular bipyramid. Mayer did not seem to distinguish between colored light and colorant though he used vermilion, [[orpiment]] (King's yellow), and Bergblau ([[azurite]]) in partially complete colorings of planes in his solid.<ref name="runge2003">{{cite web |last1=Kuehni |first1=Rolf G. |title=Philipp Otto Runge's Color Sphere A translation, with related materials and an essay |url=http://www.iscc-archive.org/pdf/RungeFarben-Kugel.pdf |archive-url=https://web.archive.org/web/20190120190655/http://iscc-archive.org/pdf/RungeFarben-Kugel.pdf |archive-date=2019-01-20 |url-status=live |access-date=2 February 2021}}</ref>{{rp|79}} [[Johann Heinrich Lambert]] (a Swiss mathematician, physicist, and astronomer) proposed a triangular pyramid with [[gamboge]], [[carmine]], and [[Prussian blue]] as primaries and only white at the top vertex (since Lambert could produce a mixture that was sufficiently black with those pigments).<ref name="renzoshamey2020"/>{{rp|123}} Lambert's work on this system was published in 1772.<ref name="Lambert1772" /> [[Philipp Otto Runge]] (the Romantic German painter) firmly believed in the theory of red, yellow and blue as the primary colors<ref name="runge2003"/>{{rp|87}} (again without distinguishing light color and colorant). His color sphere was ultimately described in an essay titled ''Farben-Kugel''<ref name="runge2003"/> (color ball) published by [[Johann Wolfgang von Goethe|Goethe]] in 1810.<ref name="runge2003"/>{{rp|84}} His spherical model of colors equally spaced red, yellow, and blue longitudinally with orange, green, and violet between them, and white and black at opposite poles.<ref name="runge2003"/>{{rp|85}}

=== Red, yellow, and blue as primary colors ===
{{redirect|Red, Blue, and Yellow|the video games|Pokémon Red, Blue, and Yellow}}

Numerous authors have taught that red, yellow, and blue (RYB) are the primary colors in art education materials since at least the 19th century, following the ideas introduced above from earlier centuries.<ref>{{cite book |last1=Osborn |first1=Laughton |year=1856 |title=Handbook of Young Artists and Amateurs in Oil Painting: Being Chiefly a Condensed Compilation from the Celebrated Manual of Bouvier ... Appended, A New Explanatory and Critical Vocabulary |publisher=J. Wiley & son |url=https://books.google.com/books?id=K81NAAAAYAAJ&dq=%22primary+colors%22+painting&pg=PA382 |language=en}}</ref><ref>{{cite book |last1=Calkins |first1=Norman Allison | year= 1888 |title=Primary Object Lessons: For Training the Senses and Developing the Faculties of Children ... |publisher=Harper & Bros. |page=195 |url=https://books.google.com/books?id=3wwUAAAAIAAJ&dq=%22primary+colors%22&pg=PA186 |language=en}}</ref><ref>{{cite book |last1=King |first1=John L. |title=Color mixing guide for artists, painters, decorators, printing pressmen, show card writers, sign painters, color mixers, give color mixtures by parts. |date=1923 |publisher=Fine Arts Publishing |url=https://archive.org/details/ColorMixingGuideForArtistsPaintersDecoratorsPrintingPressmenShow/page/n3/mode/2up |language=English}}</ref>

A wide variety of contemporary educational sources also describe the RYB primaries. These sources range from children's books<ref>{{cite book |last1=Vance |first1=Cynthia |title=Red, yellow, blue, and you |date=2008 |publisher=Abbeville Kids |location=New York |isbn=978-0-7892-0969-6 |edition=1st}}</ref> and art material manufacturers<ref>{{cite web |title=Crayola Support FAQ-What are the primary colors? |url=https://www.crayola.com/faq/another-topic/what-are-the-primary-colors/ |website=www.crayola.com |quote=What are the primary colors? Primary colors include red, blue, and yellow. Primary colors cannot be mixed from other colors. They are the source of all other colors. |access-date=2021-02-21 |archive-date=2021-04-14 |archive-url=https://web.archive.org/web/20210414105715/https://www.crayola.com/faq/another-topic/what-are-the-primary-colors/ }}</ref> to painting<ref>{{cite book |last1=Pitcher |first1=Colette |title=Watercolor Painting For Dummies |date=16 March 2011 |publisher=John Wiley & Sons |isbn=978-1-118-05200-6 |url=https://books.google.com/books?id=m_eu_9qDLhUC&q=%22primary%20colors%22%20 |language=en}}</ref> and color guides.<ref>{{cite book |title=Color Choices |author=Stephen Quiller |publisher=Watson–Guptill |year=2002 |isbn=0-8230-0697-2 |url=https://books.google.com/books?id=jiUTZQj_v5QC&dq=what-is-a-color-wheel+spaced+red+yellow+blue&pg=PA12 }}</ref> Art education materials often suggest that RYB primaries can be mixed to create ''all'' other colors.<ref>{{cite web
| title = Color
| url = https://www.nga.gov/education/teachers/lessons-activities/elements-of-art/color.html
| website = www.nga.gov
| access-date = 10 December 2017
| quote = "Red, blue, and yellow are the primary colors. With paints of just these three colors, artists can mix them to create all the other colors."
| archive-date = 11 December 2017
| archive-url = https://web.archive.org/web/20171211105219/https://www.nga.gov/education/teachers/lessons-activities/elements-of-art/color.html
}}</ref><ref>{{cite book |last1=Leidtke |first1=Amy |title=Leonardo's Art Workshop: Invent, Create, and Make STEAM Projects like a Genius |date=20 November 2018 |publisher=Rockport Publishers |isbn=978-1-63159-522-6 |url=https://books.google.com/books?id=GvF6DwAAQBAJ |language=en}}</ref>

====Criticism====
[[Albert Henry Munsell|Albert Munsell]], an American painter (and creator of the early 20th century [[Munsell color system]]), referred to the notion of RYB primaries as "mischief", "a widely accepted error", and underspecified in his book ''A Color Notation'', first published in 1905.<ref>{{cite book |last1=Munsell |first1=A.H. |title=A Color Notation |date=1907 |url=http://www.gutenberg.org/files/26054/26054-h/26054-h.htm |quote=The wide discrepancies of red, yellow, and blue, which have been falsely taught as primary colors, can no more be tuned by a child than the musical novice can tune his instrument. Each of these hues has three variable factors (see page 14, paragraph 14), and scientific tests are necessary to measure and relate their uneven degrees of Hue, Value, and Chroma.}}</ref>

Itten's ideas about RYB primaries have been criticized as ignoring modern color science<ref name="renzoshamey2020"/>{{rp|282|quote=For a three-dimensional model, Itten ignored the quantitative systems produced by Munsell and Ostwald and used a simple sphere externally resembling the one published by Runge in 1810.}} with demonstrations that some of Itten's claims about mixing RYB primaries are impossible.<ref>{{cite journal |last1=Hirschler |first1=Robert |last2=Csillag |first2=Paula |last3=Manyé |first3=Pablo |last4=Neder |first4=Mônica |title=How much colour science is not too much? |journal=Color Research & Application |quote=One of the most typical problems is that of trying to reproduce Itten's colour circle following his instructions. Students may get frustrated, because it is simply not possible to achieve acceptable results using the RYB 'primaries'. Figure 16 illustrates why it is impossible to reproduce Itten's colour circle following strictly his instructions. |date=December 2018 |volume=43 |issue=6 |page=987 |doi=10.1002/col.22275|s2cid=125461782 }}</ref>

== See also ==
* [[Color vision]]
* [[RGB color model]]
* [[RYB color model]]
* [[Unique hues]]

{{clear}}

== References ==
{{Reflist}}

{{Color topics}}
{{Photography}}
{{Authority control}}

[[Category:Primary colors| ]]
[[Category:Color]]