Veterinary ophthalmologists are often asked, "How well do animals see?" Visual function involves a combination of many factors, including: the field of view, depth perception, acuity, perception of motion, and color differentiation. All of these functions must then be integrated by the brain to produce useful vision. Although we are unable to ask our pets to read an eye chart, through comparative studies, it is possible to make some educated assumptions about their vision.
Most humans have the ability to see all the different colors of the electromagnetic spectrum, and consequently perceive all its' colors. Man's best friend is colorblind, but, fortunately, his survival does not depend upon the ability to see colors. His keen sense of smell compensates for his inability to see colors, and enables him to differentiate between things.
Extensive scientific testing on dogs supports the conclusion that they live in a colorless world. The testing done primarily focused on the dogs' responses to colors for food. Dogs could not tell the difference between one color, a signal for food, and other colors, that were not for food. Similar tests conducted on cats produced similar results, which led scientists to conclude that they, too, are colorblind and live in a gray world.
The inability of most animals to see colors, from an evolutionary standpoint, is quite simple to understand. Many colorblind animals have dull-colored coats, hunt for food in the dark of night, or graze in the dim twilight hours. Their other senses have developed to the point where the lack of color vision in no way impairs them. For them, life in a colorless world is neither a handicap, nor a threat to their survival.
The only animals, other than man, scientists can conclusively say have color vision are monkeys and apes. Both can be trained to open a colored door, behind which is food, and man can be trained to open a refrigerator door of any color!