Canine colour vision is much less rich than ours. Dogs have only two different kinds of cone cells in their retina, compared with our three. They also have far fewer of them. Where we see the rainbow as red, orange, yellow, green, blue and violet, they see only a brownish yellow that shades through yellow, grey, into light blue and blue.
Our colour vision evolved to allow us to tell when fruit was ripe and to help identify poisonous berries.
For a carnivore, that’s less important, while the space for extra rod cells allows for far more accurate spatial perception. Most mammals see only two primary colours and are generally red-green colour-blind. However, there are some birds that can see four primary colours.
Answered by Luis Villazon