Can dogs see color? A study conducted at the University of California, Santa Barbara by Jay Neitz, tested the color vision of dogs. Neitz confirmed that dogs actually do see color, but many fewer colors than normal humans do. Test of color matching indicate that the dog retina contains two classes of cone photoreceptors with spectral peaks of about 429 nm and 555 nm. A human with normal color vision has three classes of cone photoreceptors with spectral peaks of 380 nm to 770 nm. Because the wavelength of orange and red ranges from 590-750 nm, these colors may appear as a very dark brownish gray or perhaps even black to a dog.
Now you know why your dog has a hard time finding his red ball in green grass.