If you ever find yourself trapped in a pen with a bull and you happen to be wearing your favorite lucky red cape (what? you don’t have a lucky cape?), never fear. You could be wearing a red hat, pants, shirt, shoes and socks and the bull likely wouldn’t bat an eyelash as long as you mind your own business. He actually doesn’t have a problem with the tomato tone - it’s the movement and antagonizing that makes him want to gore the matador (can you blame him?).
Mythbusters dispelled the rumor when they tested flags of various colors by attaching them to matador dummies in a faux bullfighting arena, then letting a bull loose to rampage. The discovery? The bull was only mildly interested in any of them and wasn’t even that terribly aggressive if the flags weren’t waved. After this test was more or less successful in disproving the myth, the gang decided to try it out on acutal humans. One of the Mythbuster assistants (Tory, for those of you who watch the show) jumped into the ring wearing all-red apparel while two cowboys moved around the ring. Despite her eye-catching attire, the bull chased the moving people, not the stationary one.
What’s more, bulls can’t really even see any color that well (they only have two color receptors), and they’re red-green color blind. So why do matadors insist on waving red cloaks about? It’s mostly showmanship and theatrics. The splash of red shows well to the cheering crowd and looks dramatic when the matador is performing his faena - the display during the third “act” when the matador runs around and basically wears the bull out before killing him. There’s an old theory that the color was chosen because it helps mask blood, but really - you think one little swatch of fabric is going to disguise the mass amounts of blood lost by the poor bull (or the unlucky matador)?
Just for fun, here’s an old Looney Tunes called “Bully for Bugs”: