The myth that bulls get angry and charge when they see red was busted some time ago. It is thought that this misconception dates back to the year 1580 and was voiced by one of the more popular writers of that time - John Lyly.
Lyly noted that you shouldn't wear red clothes if you were trying to get close to a bull and also advised those who for whatever reason were trying to get close to an elephant, not to wear flashy and brightly colored clothes.
In the meantime, in Europe they decided to have matadors wave a red cape in front of the aggressive animal's face; the color was chosen so that the bull's blood wouldn't be as obvious when the time came for it to be killed at the end of the bullfight.
In fact, similar to rats, hippos, owls and anteaters, bulls are color blind. What infuriates them in the arena is the noise of the crowd and the cape that matadors taunt them with.