Cartoons and bullfighting posters made the rule look obvious: wave anything red and a bull loses its mind. The science of cattle vision does not cooperate. Bulls are red-green colorblind, so a crimson cape does not look specially angry to them. What sets them off is the motion of the cloth, which is why they charge pink or yellow capes just as hard.
What you were taught
Bulls are enraged by the color red
What we know now
Cattle are dichromats: they lack the cone cells humans use to see red, so a red cape looks dull yellowish-gray rather than a rage trigger. Matadors' red muleta is traditional and helps hide blood from spectators; bulls also charge the larger, often pink-and-gold capote used earlier in the fight. The threatening waving motion of the cape, not its hue, is what drives the charge.
Updated understanding emerged around 2012
Yes — and not as a joke question on a quiz. This science claim showed up in textbooks, worksheets, and classroom posters through the 2010s, which is why so many people still remember it as settled fact long after the science moved on.
No. Cattle are dichromats: they lack the cone cells humans use to see red, so a red cape looks dull yellowish-gray rather than a rage trigger. Matadors' red muleta is traditional and helps hide blood from spectators; bulls also charge the larger, often pink-and-gold capote used earlier in the fight. The threatening waving motion of the cape, not its hue, is what drives the charge. If you want the primary citation, start with WTAMU - What is it about red that makes bulls so angry?
The evidence had largely shifted by around 2012. Schools don't flip overnight, though — plenty of classrooms kept teaching the older version for years after researchers had already moved on.
2010s · Science
2010s · Science
2010s · Science