Here's the breakdown:
* Red capes aren't the issue: Bulls are colorblind, so they don't see red any differently than other colors. It's the *movement* that triggers their aggression.
* Instinctual behavior: Bulls are prey animals and have a strong instinct to defend themselves. The sudden, unpredictable movements of a cape or matador can be perceived as a threat.
* Agitation and frustration: In bullfights, the matador's movements are designed to agitate and frustrate the bull, making it more likely to charge. The cape itself is just a tool to provoke a reaction.
In summary: Bulls are more likely to react aggressively to sudden, unpredictable movements, which they interpret as a threat. The color red is irrelevant to their behavior.