Dogs are not color blind, but color weak. They are not as sensitive to brightness and hue as humans; the colors they can see are mainly yellow, blue, and gray. Colors that are difficult for dogs to distinguish are red, green, and orange. So the lawn looks yellow or light blue to dogs, and the red flowers look brown-black to dogs.

Causes of color weakness in dogs

Documents published in the Journal of the American Veterinary Medical Association in 1995 showed that the dog’s retina also has rods and cones. Therefore, it has long been considered that only Dogs that can see in black and white can actually see in color.
But because humans have three types of cones, they allow us to see all colors in the spectrum. Dogs only have two types of cones, which can only distinguish black, white, gray, blue, purple, etc. well, but cannot distinguish red, green, etc.
The dog's retina has a large number of rod cells. These cells can distinguish between gray and gray as long as there is weak light, so the dog's night vision ability is better than that of humans.
However, dogs are myopic. When converted into degrees, it is about 150 degrees, which means that dogs’ vision is about 1/5 to 1/3 of normal people. Although their eyesight is not that great, dogs have a wider field of vision than humans. Human vision is about 160-180 degrees, while dogs reach 200-290 degrees.

How guide dogs distinguish traffic lights

Guide dogs do not judge based on color when passing traffic lights. Red and green are both gray in their eyes. It can distinguish between gray light and dark, so that traffic lights can be correctly judged.