Blind Kitty Jack

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.