Researchers showed a series of videos to 42 experienced Tae Kwon Do referees.
When watching the originals, they gave the red fighters like the one on the right an average of 13 percent more points.
But when the colors were reversed, they awarded more points to the other fighter. The original losers became the winners.
The international study published in the Journal Psychological Science, is the latest of several studies on the subconscious effects of seeing red.
Professor Andrew Elliot, who's studied the effect, believes it could be an evolutionary adaptation.
"Red might have a similar effect on humans that it has in the wild in primates. So in certain primates, red is a dominant or superiority cue," said Elliot.
And it might not just affect judges and referees. Elliot thinks it might also impact an opponent. Since, red could instill fear or avoidance in their subconscious.
"Wearing red could have a positive effect on your teams performance, because the opposing team is looking at the red that you're wearing," said Elliot.
Still the effect may also have its limitations. In the case of the Tae Kwon Do judges, the bias toward red was most pronounced when the matches were close, but tapered off when one fighter was simply much better than the other.