Many animals, including dogs and cats, have a reflective layer behind the retina called the tapetum lucidum. Unlike human red-eye, which is associated with flash light reflecting from the back of the eye and blood-rich tissue, this layer reflects light back through the retina to improve low-light vision.

That extra reflective layer can produce eyeshine in photos and is why animals often appear green, yellow, or blue-green rather than red. In other words, the different color is mainly due to different eye anatomy, not because their blood is a different color.