Does red really make bulls go crazy?
Actually, bulls are at least partially colorblind. What irritates a bull about a red cape being waved in its face is that someone is waving a cape in its face at all! Yet many bulls aren’t that bothered by things being waved in their faces. Bulls are bred for fighting, and when they are about 3 years old, the ones bad-tempered enough to be interesting in a bullfight are selected.
Color vision is a tricky subject. In our eyes, we have rods that sense light but don’t provide any information about color. They do, however, work well in dim light and are essentially all we use to see at night - hence, the lack of color perception as it gets dark.
Our rods are complemented by three types of cone cells, each sensitive to different wavelengths of light - bands of what one would roughly call red, green, and blue. Any color that we know can be represented as some combination of these basic colors. When something goes wrong with this aspect of vision, it produces color-blindness, which usually isn’t a complete inability to distinguish colors but rather a narrowed range of colors that can be perceived.
While human-like color vision is common in fish, reptiles, amphibians, and birds, it’s an ability that is surprisingly rare in mammals - it’s pretty much us and the other primates. But some animals see more colors than we can - bees, for example.
Ask Dr. Knowledge is written by Northeastern University physicist John Swain. E-mail questions to firstname.lastname@example.org.