Can wearing red help you win? At the 2004 Olympics, athletes in some fighting sports wore red or blue. Fighters in red won a little more often, especially in close matches.

But later, a study showed referees videos of the same fights. Only the colors were changed. The referees gave more points to the fighter in red. So the referees' eyes may be part of the reason.

In 2005, a paper in the journal Nature reported that at the 2004 Athens Olympics, competitors wearing red won slightly more often than those in blue in four combat sports, including boxing and taekwondo. The difference was clearest in close matches. The researchers suggested that red may signal strength, as it does in some animals.

However, critics soon responded. In judo, where athletes wear white or blue, one team found that blue seemed to win more often, although other studies did not confirm this. Then, in 2008, experienced taekwondo referees watched videos in which only the colors of the fighters' gear were digitally switched. They gave more points to the same fighter when he wore red.

Does red help athletes win? In 2005, a paper in Nature looked at four combat sports at the 2004 Athens Olympics: boxing, taekwondo, and Greco-Roman and freestyle wrestling. Competitors are assigned red or blue regardless of ability, so the setting resembled a natural experiment. In all four sports, those in red won slightly more often, and the advantage was clearest in closely matched bouts.

The authors proposed that red, a signal of dominance in many animals, might intimidate opponents or boost the wearer. Challenges came quickly. A rival team reported that in judo, where athletes wear white or blue, blue seemed to have an edge, which would point to visibility, not the meaning of red.

Later studies failed to confirm it. The most telling test came in 2008. Forty-two experienced taekwondo referees scored video clips in which only the colors of the protective gear had been digitally swapped, and they gave more points to the same performance when it was shown in red. So part of the red advantage may lie with the judges, not the athletes. A 2018 meta-analysis also found that the effect behind a related claim, that red makes people more attractive, was smaller than first reported.