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The four pigments in a bird's cone cells (in this example, estrildid finches) extend the range of color vision into the ultraviolet. [1]Tetrachromacy (from Greek tetra, meaning "four" and chroma, meaning "color") is the condition of possessing four independent channels for conveying color information, or possessing four types of cone cell in the eye.
The human eye's red-to-green and blue-to-yellow values of each one-wavelength visible color [citation needed] Human color sensation is defined by the sensitivity curves (shown here normalized) of the three kinds of cone cells: respectively the short-, medium- and long-wavelength types.
Birds, however, can see some red wavelengths, although not as far into the light spectrum as humans. [46] It is a myth that the common goldfish is the only animal that can see both infrared and ultraviolet light; [47] their color vision extends into the ultraviolet but not the infrared. [48]
Unique hues have also been shown to change over the course of the year as a result of adaptation to differences in the color spectrum of the environment in summer compared to winter, [25] and have been shown to change after surgery to remove cataracts. [26]
Trichromatic color vision is the ability of humans and some other animals to see different colors, mediated by interactions among three types of color-sensing cone cells. The trichromatic color theory began in the 18th century, when Thomas Young proposed that color vision was a result of three different photoreceptor cells.
Dichromacy in humans is a form of color blindness (color vision deficiency). Normal human color vision is trichromatic, so dichromacy is achieved by losing functionality of one of the three cone cells. The classification of human dichromacy depends on which cone is missing: Protanopia is a severe form of red-green color blindness, in which the ...
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The spectrum does not contain all the colors that the human visual system can distinguish. Unsaturated colors such as pink, or purple variations like magenta, for example, are absent because they can only be made from a mix of multiple wavelengths. Colors containing only one wavelength are also called pure colors or spectral colors. [8] [9]