Many people think bulls get angry when they see a red cape. Others say, "Bulls cannot see colors, so this is wrong."

But neither idea is quite right. Cows can see some colors. In tests, young cows could tell red from blue and green. But there is no proof that red makes bulls angry. Bulls probably run at the cape because it moves.

A bullfighter waves a red cape, and the bull runs straight at it. Many people think the color makes the bull angry. Others say cattle cannot see color at all. Both ideas are wrong. In 1998, American researchers found that cows have two types of color-sensing cells called cones. Humans have three.

So cattle can see some colors, but not as many as we can. In a 2001 experiment, calves could tell red from blue or green, even when the lights were equally bright.

But no study has shown that red itself makes bulls angry. In bullfights, bulls also charge at pink and yellow capes. The movement of the cape probably matters more than its color.

Ask why a bull charges at a matador's red cape, and someone will usually reply that cattle are color-blind anyway. That popular correction is itself mistaken. In 1998, researchers recorded the responses of the retina in cows, goats and sheep.

All three species had two types of cones, one most sensitive to blue light at around 444 to 455 nanometers and the other to yellowish-green light at around 552 to 555 nanometers. Cattle therefore have dichromatic vision. Their world is not black and white but roughly comparable to that of a person with red-green color deficiency.

Behavioral tests agree. In a 2001 study in which the lights were matched for brightness, calves picked out red from blue or green with an average accuracy of 82 to 89 percent, though they had trouble separating blue from green.

So cattle can see red. There is no good evidence, however, that red makes them aggressive. Calves were sometimes more active under red light, but only in particular conditions, such as unfamiliar surroundings. Few controlled studies have been run inside a bullring. Even so, bulls are known to charge at pink and yellow capes as well, so movement is the more likely trigger.