When a referee sees red...

It has been shown that wearing red sports attire has a positive impact on one's outcome in combat sports such as tae kwon do or wrestling. One speculation has been that this is due to an evolutionary or cultural association of the color red with dominance and aggression, with this association triggering a psychological effects (dominance/submission) in the competitors. Hagemann et al. offer evidence that perceptual bias in the referee is the more likely explanation, by showing that when tae kwon do referees watch videos of matches in which the competitors wear either read or blue protective gear:

The competitor wearing red protective gear was awarded an average of 13% (0.94 points) more points than the competitor wearing blue protective gear. The number of points awarded increased for a blue competitor who was digitally transformed into a red competitor, and decreased for a red competitor who was digitally transformed into a blue competitor.