Imagine you are an experienced martial arts referee. You are asked to score a number of taekwondo bouts, shown to you on video. In each bout, one combatant is wearing red, the other blue. Would clothing colour make any difference to your impartial, expert judgement? Of course it wouldn't. Yet research shows it almost certainly would. Last year sports psychologists at the University of Münster, Germany, showed video clips of bouts to 42 experienced referees. They then played the same clips again, digitally manipulated so that the clothing colours were swapped.
The result? In close matches, the scoring swapped too, with red competitors awarded an average of 13 per cent more points than when they were dressed in blue. "If one competitor is strong and the other weak, it won't change the outcome of the fight," says Norbert Hagemann, who led the study. "But the closer the levels, the easier it is for the colour to tip the scale." This is just the latest piece of research suggesting that exposure to certain colours can have a significant effect on how people think and act. The powerful influence of colour on sporting success was discovered a few years ago, when evolutionary anthropologists Russell Hill and Robert Barton of Durham University, UK, were looking for some way to test the idea that colours influence human behaviour.
The 2004 Athens Olympics were coming up, and it dawned on them that in some Olympic fighting sports - boxing, taekwondo, Graeco-Roman wrestling and freestyle wrestling - competitors are randomly assigned a red or blue kit. "We realised that this was a ready-made experiment to study the effects of colour on match outcome," Prof Barton says. When they analysed the results they found that shirt colour appeared to influence the result, with nearly 55 per cent of bouts being won by the competitor in red. In closely fought bouts it was 62 per cent. "It should have been roughly 50 per cent red, 50 per cent blue, and this was a statistically significant deviation," Prof Barton says. "When fights were relatively symmetrical, colour tipped the balance."
Red also appears to exert its influence in team games. Last year, a study of 56 seasons of English football, led by Martin Attrill at the University of Plymouth, UK, found that, on average, teams whose first-choice kit was red finished higher in the league and won more home games than teams in other colours - which might go some way to explaining why Liverpool, Manchester United and Arsenal have won 38 out of 63 league titles between them since the Second World War.
Clearly the effect of wearing red is strong enough to tip the balance of fights and football matches, but where did it originate? One possibility is that red is simply easier to see than other colours. But most researchers believe that red directly affects how you perceive the wearer of that colour. In nature, red is often used to signal dominance and aggression, and in humans this is reinforced by cultural symbols such as warning signs and stop signals.
Primate behaviour is strongly influenced by red. Joanna Setchell of Durham University found that mandrills, the world's largest species of monkey, use colour as a means of conflict management. In males, red faces, rumps and genitalia act as a status symbol, communicating fighting ability. Other primates use more subtle variations in facial redness to signal dominance. Rhesus monkeys, for example, become redder in the face in the mating season.
Recent evidence supports the idea that red exerts its effect on humans via perceptions of dominance. In an experiment, Prof Hill and his colleague Tony Little showed 105 volunteers different coloured circles and asked them to indicate which would be "most likely to win a physical competition" and which circle looked "most dominant". Red won hands down. In a remarkable series of studies, Andrew Elliot of the University of Rochester in New York has demonstrated that even a brief glimpse of red can change human abilities and behaviour in all sorts of ways.
In one experiment, volunteers were asked to carry out a five-minute IQ test. They were assigned a bogus "participant number", written in either red or black, on the corner of the test paper. Volunteers whose numbers were written in red scored consistently lower on the tests. Prof Elliot also gave the students different coloured folders and asked them to choose their preferred level of difficulty for an IQ test. Students given red folders tended to choose easier tests.
Even more remarkably, Prof Elliot has found that viewing red for just a few seconds can make people more timid. Prof Elliot's team told 67 students that they would be taking either a vocabulary test or an analogies test, and asked them to look inside a folder to find out which one. The students saw either the word "analogies" or the word "vocabulary" on a red or green background - and the colour had a profound effect on their subsequent behaviour. When the students were instructed to walk to an adjacent laboratory to take the test, they found a sign on the door saying "Please knock". Those who had seen a red background knocked fewer times, and more quietly, than those given green.
Red does not always affect us through its association with danger. When Prof Elliot and his colleague Daniela Nesta showed male volunteers photos of averagely attractive women on red and white backgrounds, the men rated the women on red as more attractive. Men asked to compare women in red or green shirts, and then red or blue shirts, said that they would be more likely to ask a red-clothed woman on a date and spend more money on that date.
"Red is clearly context specific. In achievement situations red means danger, which leads to avoidance, but in romance situations red means sexual availability or romance and that leads to approach behaviour," says Prof Elliot. It is this context-specificity that Prof Elliot and his colleagues are now exploring. "Given that the influence of colour on our behaviour is so prevalent, it's shocking that we aren't more aware of it."