Bulls, along with all other cattle, are color-blind to red. Thus, the bull is likely irritated not by the muleta ’s color, but by the cape’s movement as the matador whips it around. In support of this is the fact that a bull charges the matador’s other cape — the larger capote — with equal fury.

Seeing the motion of a red cape triggers a bull’s instinct to charge against the potential threat. This ingrained reaction aids bullfighters facing bulls in the ring. Bullfighters rely on red capes to trigger bulls to charge and enable them to enact their maneuvers.

In a bullfighting context, the aggressive behavior of the bull is not primarily triggered by the color red but by the movement of the cape and the actions of the matador. Bulls are naturally territorial and defensive animals, and the presence of the matador, along with the cape's movements, can provoke them to charge.