Everyone says a bull goes wild at the colour red, but it is not true, and the reason is surprising: a bull cannot really see red at all. Bulls are red-green colourblind, so a bright red cape looks dull and greyish to them, nothing special. What actually sets a bull off is the cape being waved about. The flapping movement looks like a threat, so the bull charges at it. And here is the giveaway: it does not matter what colour the cape is. Wave a blue one, a green one or a white one and the bull charges just the same. Hold a red cape perfectly still and the bull will mostly ignore it. So why do matadors use red? Mainly so the blood does not show up so much. In the simulator you can pick a cape colour, wave it or hold it still, and switch on bull vision to see how dull that red really looks to the bull.
Most people think bulls are enraged by the colour red. In fact bulls are red-green colourblind and see red as dull; what triggers a charge is the cape's movement, and a waved cape of any colour works just as well.
What's actually happening
It is one of the most repeated animal facts there is: show a bull a red cape and it sees red, in every sense, and charges. The image is everywhere, from cartoons to the phrase like a red rag to a bull. There is just one problem. A bull cannot see red the way you can. Cattle are red-green colourblind, what scientists call dichromats, because their eyes carry only two types of colour-detecting cone instead of our three. To a bull, a brilliant scarlet cape does not blaze; it reads as a muddy, dull yellow-grey, no more eye-catching than the dirt of the ring. The one colour the myth is built on is precisely the colour the animal is worst at seeing.
So if not the colour, what makes a bull charge? Movement. In the ring the matador swirls and snaps the cape, the muleta, through the air, and that sudden, sweeping motion is what the bull reacts to. A large moving object coming at it, or fluttering nearby, looks like a challenge to be met head-on, and the bull does what an alarmed bull does: it charges the moving thing. The proof is simple and has been shown many times. Wave a cape that is blue, or green, or plain white, and the bull goes for it just as readily. Hold the red cape dead still, and the bull loses interest and often just stands there. If the colour were the trigger, none of that would happen. It is the motion the whole time, with the colour along for the ride.
Why, then, the famous red? Tradition and practicality, not biology. Red has long been the colour of the muleta in Spanish bullfighting, and it has one genuinely useful property: it hides the blood. As a fight goes on and the bull is wounded, a red cloth keeps the stains from showing as starkly to the crowd. That is the whole of red's role, a stagecraft choice, not a button that enrages the animal. The myth endures because we always see the two things together, the red cape and the charging bull, and our brains stitch them into cause and effect. Switch on bull vision in the simulator and the illusion falls apart: the red goes flat and dull, while a still cape of any colour leaves the bull unmoved and a waved one of any colour sends it charging.
Bulls do not hate red and barely see it; it is the cape's motion that makes them charge, and red is used only by tradition and to hide blood.
- 1Notice that a cat or dog often pounces on a fast-flicked toy or string but ignores the very same toy lying still, whatever its colour.
- 2Try flicking a plain, dull-coloured cloth quickly versus holding a bright one motionless near a playful pet.
- 3The movement, not the colour, is what grabs the attention, exactly the principle behind a bull charging a waved cape of any colour.
Common questions
Not the way we do. Cattle are dichromats, effectively red-green colourblind, so a bright red cape looks like a dull yellow-grey to them rather than a striking colour.
The movement of the cape. The matador swirls and snaps the cloth, and the bull reacts to that motion as a threat. A waved cape of any colour provokes a charge, while a still cape is largely ignored.
Tradition, and because red usefully hides bloodstains as the fight goes on. The colour itself plays no part in enraging the bull; it is a stagecraft choice.