Dogs are not color blind, but color weak. There are two types of cones in the dog's retina. They can only sense blue light (short wavelength light waves) and red and yellow light (medium and long wavelength light waves). Therefore, dogs are not completely color blind, but color weak.

Scientist experiments have verified that dogs can see blue, yellow and gray, but purple is not visible to them Their eyes are blue, red is dark gray and black in their eyes, blue-green is gray in their eyes, and orange, yellow, and green are the three colors of dogs’ visual blind spots.