<unk>  is the condition of possessing three independent channels for conveying color information, derived from the three different cone types. Organisms with<unk>  are called trichromats.
The normal explanation of<unk>  is that the organism's retina contains three 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 three, since different types may be active at different light intensities.  In vertebrates with three types of cone cells, at low light intensities the rod cells may contribute to color vision, giving a small region of tetrachromacy in the color space.
Humans and other closely related primates are usually trichromats, as are female New World monkeys of most species, and both male and female howler monkeys.  Recent research suggests that<unk>  may also be quite general among marsupials.  Most other mammals are currently thought to be dichromats, with only two types of cone (though the possibility of limited<unk>  at low light levels where the rods and cones are both active).  Some species of insects (such as honeybees) are also trichromats, being sensitive to ultraviolet, blue and green instead of blue, green and red.
Trichromacy
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