Colors

While most humans aretrichromatic(having three types of color receptors), many animals, known astetrachromats, have four types. These include some species ofspiders, mostmarsupials,birds,reptiles, and many species offish. Other species are sensitive to only two axes of color or do not perceive color at all; these are calleddichromatsandmonochromatsrespectively. A distinction is made betweenretinal tetrachromacy(having four pigments in cone cells in the retina, compared to three in trichromats) andfunctional tetrachromacy(having the ability to make enhanced color discriminations based on that retinal difference). As many as half of all women are retinal tetrachromats.[13]:p.256The phenomenon arises when an individual receives two slightly different copies of the gene for either the medium- or long-wavelength cones, which are carried on theX chromosome. To have two different genes, a person must have two X chromosomes, which is why the phenomenon only occurs in women.[13]There is one scholarly report that confirms the existence of a functional tetrachromat.[14]SynesthesiaIn certain forms ofsynesthesia-ideasthesia, perceiving letters and numbers (grapheme–color synesthesia) or hearing musical sounds (music–color synesthesia) will lead to the unusual additional experiences of seeing colors. Behavioral andfunctional neuroimagingexperiments have demonstrated that these color experiences lead to changes in behavioral tasks and lead to increased activation of brain regions involved in color perception, thus demonstrating their reality, and similarity to real color percepts, albeit evoked through a non-standard route.AfterimagesAfter exposure to strong light in their sensitivity range,photoreceptorsof a given type become desensitized. For a few seconds after the light ceases, they will continue to signal less strongly than they otherwise would. Colors observed during that period will appear to lack the color component detected by the desensitized photoreceptors. This effect is responsible for the phenomenon ofafterimages, in which the eye may continue to see a bright figure after looking away from it, but in acomplementary color.Afterimage effects have also been utilized by artists, includingVincent van Gogh.Color constancyMain article:Color constancyWhen an artist uses a limitedcolor palette, theeyetends to compensate by seeing any gray orneutral 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 appearas a variety of green, a mixture of red and black will appear as a variety of purple, and pure gray will appear bluish.[15]The trichromatic theory is strictly true when thevisual system is in a fixed state of adaptation. 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 byEdwin Landin the 1970s and led to his retinex theory ofcolor constancy.Both phenomena are readily explained and mathematically modeled with modern theories of chromatic adaptation and color appearance (e.g.CIECAM02, iCAM).[16]There is no need todismiss 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.Color namingMain article:Color termSee also:Lists of colorsandWeb colorsColors vary in several different ways, includinghue(shades ofred,orange,yellow,green,blue, andviolet),saturation,brightness, andgloss. Some color words are derived from the name of an object of that color, such as "orange" or "salmon", while others are abstract, like "red".In the 1969 studyBasic Color Terms: Their Universality and Evolution,Brent BerlinandPaul Kaydescribe a pattern in naming "basic" colors (like "red" but not "red-orange" or "dark red" or "blood red", which are "shades" of red). All languages that have two "basic" color names distinguish dark-cool colors from bright-warm colors. The next colors to be distinguished are usually red and then yellow or green. All languages with six "basic" colors include black, white, red, green, blue, and yellow. The pattern holds up to a set of twelve: black, gray, white, pink, red, orange, yellow, green, blue, purple, brown, andazure(distinct from blue inRussianandItalian, but not English).AssociationsIndividual colors have a variety of cultural associations such asnational colors(in general described in individual color articles andcolor symbolism). The field ofcolor psychologyattempts to identify the effects of color on human emotion and activity.Chromotherapyis a form ofalternative medicineattributed to various Eastern traditions. Colors have different associations in different countries and cultures.[17]Different colors have been demonstrated to have effects on cognition. For example, researchers at the University of Linz in Austria demonstrated that the color red significantly decreases cognitive functioning in men.
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