Part of the show Naked Science Question and Answer
Les in Peterborough asked:
People say that dogs are colour-blind. Is that a fact?
It depends on how you define colour-blind. The version of that urban myth that I've heard is that they see in black and white, and that's just not true. If you look at a dog's retina, the thing that turns light into neurochemistry or electrical signals, there are structures in the dog's retina called cones. These are identical to structures in the human retina called cones that can see coloured parts of the visual system. So dogs can definitely see colours. But if you analyse those cones, they paint a very different picture of what dogs see of the world than what humans do. The best description is that dogs are the equivalent of human red-green colour blindness. So they have a spectrum of colours that means they are pretty good at seeing greens, violets and blues, but at the red end of the spectrum they're less good. They probably appreciate it as a slightly different colour, such as yellow. But they're certainly not colour blind.