Blue: the colour of cold and loneliness. Proud and dignified, yes. But ferocious? Intimidating? Not usually. So Rangers fans anxiously awaiting tonight's game in Greece tonight may be encouraged to hear that wearing blue has been found to offer sportsmen a competitive, combative advantage.

In a study of judo matches at the 2004 Athens Olympics, blue players won significantly more matches than their white competitors because, say researchers, the blue may have an "intimidating" effect.

The results were a shock. If you were looking for a colour to strike fear into your opponent, there is no contest. Red was the colour Bill Shankly chose to turn his Liverpool men into "monsters". Tiger Woods wears red on the last day of every major golf tournament. And it was not entirely surprising when an analysis of 2004 Olympic boxing, Tae Kwon Do and wrestling matches found that red contestants won more often.

When new-coloured judo uniforms were introduced, blue was considered a fair choice. But not so, according to a study by Candy Rowe of Newcastle University, published in Nature, which has sparked both debate and criticism in the sporting and scientific communities.

Anyone doubting that butch judo athletes could somehow be spooked by the hue of their adversary's robe would do well to listen to David Matsumoto, a judo champion and instructor turned psychology professor at San Francisco State University, who carried out a separate study. "If you talk to judo players, some of them will tell you they feel different when they wear blue than white. They're not used to it, and they find it unsettling - that might give them the edge that makes them more aggressive."

To dig deeper, Matsumoto did a more detailed study of the four biggest international judo contests since the blue uniform was introduced. The blues consistently won more matches - 60% in the medal rounds - but interestingly only in male competition. Robe colour made little difference to women. The winning edge for blue was greatest in the later rounds of competition - and over the years, the gap between blue and white has widened.

"It may be that wearing blue makes athletes more aggressive," says Matsumoto, "or it could be that judges perceive them to be more aggressive, and award higher scores. Separate colours may be a good thing for the spectator, but if there really is a bias towards the athlete we have to find a way of correcting that."

So how could colour have such a profound influence on our competitive psychology? The answer may lie in instinctive behaviours we have evolved over millions of years. Human faces turn red with blood when we become aggressive. In the animal world, both red and blue are thought to be related to fitness, aggression and high levels of testosterone.

Could it really be, then, that pulling on a blue or red vest signals high levels of testosterone, striking fear into the opposing side? Although the red shirts worn by the players of Manchester United, Arsenal and Liverpool are clearly no longer the overriding reason for their dominance, historically it may have played a part in a team's success, says Paul Preenan, of Amsterdam University. "It could be that red helps intimidate opponents," he explains. "It could be that referees favour red and don't penalise red teams so much. It could also be that football crowds favour red more and cheer louder for their team."

The evidence for scrapping blue in judo is less convincing, says Preenan, who, with Peter Dijkstra of Glasgow University, has just published a study of 72 major judo tournaments.

The studies by Rowe and Matsumoto were flawed, they claim, because even in later rounds of the tournament, the blue uniform was still more likely to be worn by the seeded athlete. Remove all games involving seeded players from the equation and the bias for blue disappears.

Their conclusion: blue and white are a fair match in sport. So, alas, it seems Rangers will have no colourful advantage in Greece tonight. What about Aberdeen, who take on Bayern Munich in Germany? The Dons may be forced to swap the red shirts which won them a famous 2-2 draw last week, because Bayern play in red at home. So could this colour the result? "Based on the research," says Preenen, "yes, I'm afraid this could have a negative impact."