“Bulls are enraged by the color red.”

The enduring image of a matador waving a scarlet cape to incite a charging bull has cemented a common misconception in the public imagination. Many people believe that the color red itself is a direct trigger for a bull's aggression, leading to the popular phrase "seeing red" to describe intense anger. This dramatic visual, central to the spectacle of bullfighting, has inadvertently served as the primary origin of the myth.

However, scientific evidence reveals that this widely held belief is untrue. Bulls are dichromats, meaning their eyes possess only two types of cone cells, which renders them red-green colorblind. They cannot distinguish red from green, perceiving them instead as shades of gray or yellow. Consequently, the vibrant red of the matador's cape, known as a muleta, is entirely irrelevant to the bull's behavior. Their aggressive responses are not to the color, but to the swift, erratic, and provocative movements of the cape, which they perceive as a threat or an invitation to charge. The traditional red color of the cape is primarily for the audience's aesthetic enjoyment and, more practically, to help mask any bloodstains during the event.

The reason this myth persists despite scientific debunking likely lies in the powerful visual narrative of the bullfight itself. For human observers, the vivid red against the backdrop of the arena and the bull's dark hide creates a compelling, albeit incorrect, association between the color and the animal's fury. This strong visual impact, coupled with generations of cultural storytelling and artistic representations, has ingrained the idea that red is inherently enraging to bulls, overshadowing the biological reality of their vision and their actual reactive triggers.