Research at the University of Münster, Germany, showed that in close martial arts matches, competitors wearing red were awarded ~13% more points compared to if they had a blue uniform.
The discovery is yet another in a string of discoveries that reveal color can affect the human mind. Red, in particular, has been studied and is believed to be perceived as a dominant color, causing the observer to perform adversely.
You can also participate in the study - see here.
But don't think the color of your uniform will make you Bruce Lee. As researcher Robert Barton points out, "If you're rubbish, a red shirt won't stop you from losing, but when fights were relatively symmetrical, colour tipped the balance."