Editing Color (section)

=== Color constancy<span class="anchor" id="Colour constancy"></span> ===
{{main|Color constancy}}
When an artist uses a limited [[color palette]], the human [[visual system]] tends to compensate by seeing any gray or neutral color as the color which is missing from the color wheel. For example, in a limited palette consisting of red, yellow, black, and white, a mixture of yellow and black will appear as a variety of green, a mixture of red and black will appear as a variety of purple, and pure gray will appear bluish.<ref>{{cite web|last=Depauw|first=Robert C.|title=United States Patent|url=http://www.google.com/patents?hl=en&lr=&vid=USPAT3815265&id=tSEzAAAAEBAJ&oi=fnd&dq=mixing+paint+colors&printsec=abstract#v=onepage&q=mixing%20paint%20colors&f=false|access-date=20 March 2011|archive-date=6 January 2012|archive-url=https://web.archive.org/web/20120106111021/http://www.google.com/patents?hl=en&lr=&vid=USPAT3815265&id=tSEzAAAAEBAJ&oi=fnd&dq=mixing+paint+colors&printsec=abstract#v=onepage&q=mixing%20paint%20colors&f=false|url-status=dead}}</ref><!-- not due to black pigment being dark blue therefore reflecting more blue light? This is a real physical phenomenon and not a perceptual one. Is this paragraph not irrelevant to color constancy? -->

The trichromatic theory is strictly true when the visual system is in a fixed state of adaptation.<ref>{{Cite journal |last=Walters |first=H. V. |date=1942 |title=Some Experiments on the Trichromatic Theory of Vision |url=https://www.jstor.org/stable/82365 |journal=Proceedings of the Royal Society of London. Series B, Biological Sciences |volume=131 |issue=862 |pages=27–50 |doi=10.1098/rspb.1942.0016 |jstor=82365 |bibcode=1942RSPSB.131...27W |s2cid=120320368 |issn=0080-4649}}</ref> In reality, the visual system is constantly adapting to changes in the environment and compares the various colors in a scene to reduce the effects of the illumination. If a scene is illuminated with one light, and then with another, as long as the difference between the light sources stays within a reasonable range, the colors in the scene appear relatively constant to us. This was studied by [[Edwin H. Land]] in the 1970s and led to his retinex theory of [[color constancy]].<ref>{{Cite web |title=Edwin H. Land {{!}} Optica |url=https://www.optica.org/History/Biographies/bios/Edwin-H--Land |access-date=2023-12-08 |website=www.optica.org}}</ref><ref>{{Cite journal |last=Campbell |first=F. W. |date=1994 |title=Edwin Herbert Land. 7 May 1909-1 March 1991 |url=https://www.jstor.org/stable/770305 |journal=Biographical Memoirs of Fellows of the Royal Society |volume=40 |pages=197–219 |doi=10.1098/rsbm.1994.0035 |jstor=770305 |s2cid=72500555 |issn=0080-4606}}</ref>

Both phenomena are readily explained and mathematically modeled with modern theories of chromatic adaptation and color appearance (e.g. [[CIECAM02]], iCAM).<ref name="CAM">M.D. Fairchild, [http://www.wiley.com/WileyCDA/WileyTitle/productCd-0470012161.html Color Appearance Models] {{webarchive|url=https://web.archive.org/web/20110505034940/http://www.wiley.com/WileyCDA/WileyTitle/productCd-0470012161.html|date=May 5, 2011}}, 2nd Ed., Wiley, Chichester (2005).</ref> There is no need to dismiss the trichromatic theory of vision, but rather it can be enhanced with an understanding of how the visual system adapts to changes in the viewing environment.