<Tr> <Td> Pentachromacy </Td> <Td> 5 </Td> <Td> 10 billion </Td> <Td> Some insects (specific species of butterflies), some birds (pigeons for instance) </Td> </Tr> <P> Color perception mechanisms are highly dependent on evolutionary factors, of which the most prominent is thought to be satisfactory recognition of food sources . In herbivorous primates, color perception is essential for finding proper (immature) leaves . In hummingbirds, particular flower types are often recognized by color as well . On the other hand, nocturnal mammals have less - developed color vision, since adequate light is needed for cones to function properly . There is evidence that ultraviolet light plays a part in color perception in many branches of the animal kingdom, especially insects . In general, the optical spectrum encompasses the most common electronic transitions in matter and is therefore the most useful for collecting information about the environment . </P> <P> The evolution of trichromatic color vision in primates occurred as the ancestors of modern monkeys, apes, and humans switched to diurnal (daytime) activity and began consuming fruits and leaves from flowering plants . Color vision, with UV discrimination, is also present in a number of arthropods--the only terrestrial animals besides the vertebrates to possess this trait . </P> <P> Some animals can distinguish colors in the ultraviolet spectrum . The UV spectrum falls outside the human visible range, except for some cataract surgery patients . Birds, turtles, lizards, many fish and some rodents have UV receptors in their retinas . These animals can see the UV patterns found on flowers and other wildlife that are otherwise invisible to the human eye . </P>

The human eye can distinguish at most 16 million colors