Blind Kitty Jack

Humans and primates are unique as they possess trichromatic color vision, and are able to discern between violet - short wave (SW), green - medium wave (MW), and yellow-green - long wave (LW) . Mammals other than primates generally have less effective two-receptor color perception systems, allowing only dichromatic color vision; marine mammals have only a single cone type and are thus monochromats. Honey- and bumblebees have trichromatic color vision, which is insensitive to red but sensitive in ultraviolet to a color called bee purple.
Other animals, such as tropical fish and birds, have more complex color vision systems than humans. There is evidence that ultraviolet light plays a part in color perception in many branches of the animal kingdom, (especially insects) though there has not been enough evidence to show this. It has been suggested that it is likely that pigeons are pentachromats. Papilio butterflies apparently have tetrachromatic color vision despite possessing six photoreceptor types. The most complex color vision system in animal kingdom has been found in stomatopods with up to 12 different spectral receptor types which are thought to work as multiple dichromatic units.
Blindness often afflicts pets, especially glaucoma in old dogs.