Dichromat

A dichromat is an organism that can match any color they see with a mixture of no more than two pure spectral lights. By comparison, a trichromat requires three pure spectral lights to match all colors in their visual spectrum. The condition of being a dichromat is called dichromacy.

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The normal explanation of dichromacy is that the organism's retina contains two types of color receptors (called cone cells in vertebrates) with different absorption spectra. In practice the number of such receptor types may be greater than two, since different types may be active at different light intensities (in other words, the absorption spectra of different types of color receptors may overlap). In vertebrates with two types of cone cells, at low light intensities the rod cells may contribute to color vision, giving a small region of trichromacy in the color space.

Trichromat: A trichromat is an organism for which the perceptual effect of any arbitrarily chosen light from its visible spectrum can be matched by a mixture of no more than three different pure spectral lights. The condition of being a trichromat is called trichromacy....

Visual spectrum: REDIRECT Visible spectrum...

Retina: The retina is a thin layer of cells at the back of the eyeball of vertebrates and some cephalopods; it is the part of the eye which converts light into nervous signals....