Scientists used to believe that dogs could only see in black and white – however recent studies have shown this to not be totally true.
Humans can see colours due to different receptor rods in the eye. We have rods to see 3 different colurs – red, blue and green. These are the primary colours and our brains can process the signals from these rods to make up all the other colours.
Dogs only have about 20% of the number of rods as humans and these are mostly in the green and blue – so they struggle to see red. In other words, dogs see the colors of the world as basically yellow, blue, and gray.
One amusing fact is that the most popular colors for dog toys today are red or safety orange. The problem, of course, is that red is difficult for dogs to see and may appear to them as a very dark brownish gray or even black. So if your dog runs right past the toy that you tossed, he may not be stubborn. He’s probably just having a hard time discriminating it from the green grass of your lawn.