Dogs are not truly color blind

Actually, the idea that dogs are color blind is not entirely correct, because dogs cannot distinguish all colors; they just have poorer ability to recognize certain colors, while they can still distinguish many other colors very well. To determine if a person is color blind, people are asked to identify simple numbers or images from a multicolored background. So how did researchers arrive at the viewpoint that dogs are color blind?

Color blindness means being able to see only part of the visible light spectrum, which limits color perception. However, this does not imply that dogs’ color perception is very limited; in other words, dogs can still distinguish many different colors. Researchers have proved this with numerous experiments.

Dogs’ retinas have two types of cone cells that can recognize short and medium-long wavelengths of light, meaning they can perceive blue light (short wavelength) and red-yellow light (medium-long wavelength). Because of the fewer cone cells, the world of color in a dog’s eyes is not as colorful as what we see. Humans have three types of cone cells that allow us to see all colors in the visible spectrum. Since dogs have only two types of cone cells, the colors they can distinguish are similar to those seen by red-green colorblind humans. But colorblind people can still see many other colors—so do dogs also see these colors? Scientists used two methods to confirm this.

Dogs Can Also Distinguish Blue, Purple, and Related Colors

One method was to shine colored light beams into dogs’ eyes to get images reflected back from their eyes. Scientists studied these reflected images, then compared them with images reflected back from human eyes under the same light.

The other method was to train dogs to "tell" scientists what they see. In experiments, scientists showed dogs several sets of colors, each containing three colors with two being the same. After a small amount of training, the dogs could use their noses to indicate the distinct color in each set to the scientists. By continuously changing the light colors and repeating the process, scientists concluded that the world in a dog's eyes is black, white, and dark gray, mixed with red-yellow light of medium-long wavelengths and blue light of short wavelengths. The world looks like a black-and-white TV picture with different brightness levels but no color variation. Guide dogs distinguish red and green traffic lights based on the difference in brightness between the two lights. Dogs have subtle ability to distinguish gray shades, and with this ability, they can perceive changes in brightness and produce stereoscopic visual images.

Dogs have relatively good ability to distinguish black, white, and gray colors. Besides these, dogs can also distinguish different shades of blue, indigo, and purple. This shows that dogs are not completely color blind as people often say; they just have weaker recognition of certain colors, so they can still distinguish a considerable number of colors.