Summary: This color alters your perception of the world. Evidence that it does, how it does, why it does and some implications are presented below.

(Overcoming Bias: Seeing Red)

Across a range of sports, we find that wearing red is consistently associated with a higher probability of winning. These results indicate not only that sexual selection may have influenced the evolution of human response to colours, but also that the colour of sportswear needs to be taken into account to ensure a level playing field in sport.¹

In the study quoted above Hill and Barton examine the outcomes of the 2004 Olympic Games in boxing, tae kwon do, Greco–Roman wrestling and freestyle wrestling. In these events competitors were for each bout randomly assigned red or blue outfits. In the matches where one side dominated the other outfit color made little difference. In close matches, however, combatants in red won over 60% percent of the time. This makes sense since there are presumably other factors that effect the outcome.

In soccer (or football, as the case might be):

Since 1947, English football teams wearing red shirts have been champions more often than expected on the basis of the proportion of clubs playing in red. To investigate whether this indicates an enhancement of long-term performance in red-wearing teams, we analysed the relative league positions of teams wearing different hues. Across all league divisions, red teams had the best home record, with significant differences in both percentage of maximum points achieved and mean position in the home league table. The effects were not due simply to a difference between teams playing in a colour and those playing in a predominantly white uniform, as the latter performed better than teams in yellow hues. No significant differences were found for performance in matches away from home, when teams commonly do not wear their “home” colours. A matched-pairs analysis of red and non-red wearing teams in eight English cities shows significantly better performance of red teams over a 55-year period.²

Of course it still isn't clear how red soccer teams win. They might have the benefit of deferential refereeing or they might be intimidating opposing teams.

Same goes for the combat sports. Hill and Barton figured that the color red had some physiological effect, perhaps increasing the testosterone levels of the player in the dominant color. But a study by Norbert Hagemann et al. suggests that the color red has a biasing effect on referees:

We propose that the perception of colors triggers a psychological effect in referees that can lead to bias in evaluating identical performances. Referees and umpires exert a major influence on the outcome of sports competitions. Athletes frequently make very rapid movements, and referees have to view sports competitions from a very disadvantageous perspective, so it is extremely difficult for them to make objective judgments. As a result, their judgments may show biases like those found in other social judgments. Therefore, we believe that it is the referees who are the actual cause of the advantage competitors have when they wear red. Because the effect of red clothing on performance and on the decisions of referees may well have been confounded in the original data, we conducted a new experiment and found that referees assign more points to tae kwon do competitors dressed in red than to those dressed in blue, even when the performance of the competitors is identical.³

By digitally altering the color of the competitor's outfit they were able to alter the judge's ruling on the outcomes. The video here shows what they did. Of course, the effect could be a product of both referee bias and intimidation.

Why does the color red have this effect? The explanation given by every single study I have seen is that we're just not that different from the rest of the animal kingdom where red is an indicator of a high position in dominance hierarchies. In short, we're like mandrills.

Male mandrills also possess rank-dependent red coloration on the face, rump and genitalia, and we examined the hypothesis that this coloration acts as a 'badge of status', communicating male fighting ability to other males. If this is the case, then similarity in color should lead to higher dyadic rates of aggression, while males that differ markedly should resolve encounters quickly, with the paler individual retreating. Indeed, appeasement (the 'grin' display), threats, fights and tense 'stand-off' encounters were significantly more frequent between similarly colored males, while clear submission was more frequent where color differences were large. We conclude that male mandrills employ both formal behavioral indicators of dominance and of subordination, and may also use relative brightness of red coloration to facilitate the assessment of individual differences in fighting ability, thereby regulating the degree of costly, escalated conflict between well-armed males.⁴

 Perhaps related is the fact that human skin becomes flushed, and thus reddish when a person is angry but when a person is afraid, they get pale. 

Now, if this effect were limited to sporting events some of us might not care. But we have no reason to think it is limited to sporting events. This phenomena could effect our beliefs on the micro level, leading us to believe someone is more of a threat than they actually are or altering our perception of a person's status. It also recommends wearing red to signal dominance and aggressiveness. Given the popularity of the hypothesis than women find men who signal social dominance more attractive someone ought to test to see if women find men in red more attractive (it actually works in reverse but probably for totally different evolutionary reasons).

More troubling, I think, is the effect this bias could have on the macro level. Consider, for example, the widespread belief among American voters that Republicans are stronger on national security and better able to protect the country. Likely most of this belief is fostered by Republican leaders using more aggressive language, the presence of a pacifist faction in the Democratic party and (of late) the Republican party's greater willingness to use military force. But perhaps some of the GOP's image as a party of strong leaders is the result of the color with which they are constantly identified. Keep in mind that a lot of voters know next to nothing about the actual differences between the parties. Which side looks stronger to you?

Or consider geopolitics and the resources that went into beating the Soviet Union which by many accounts was never a serious economic or military rival of the United States. And consider how scared Americans were of the "red menace".

Obviously there were plenty of incentives for Americans to be scared and for politicians to scare Americans. And it isn't the case that the USSR was no threat to the US at all. But politics appears to be a sphere of human activity where symbolism is important. America's perception of the Soviet Union as a dominant and aggressive foe probably increased the chances of armed conflict. And given that the conflict between the US the USSR came close to nuclear exchange it seems plausible that communism's choice in hue was responsible for increasing (albeit slightly) the probability of a lot of people dying.

China's color is red as well.

by Jack Noble

¹ Red enhances human performance in contests, Russell A. Hill & Robert A. Barton, Nature 435, 293 (19 May 2005).

² Attrill, Martin J., Karen A. Gresty, Russell A. Hill and Robert A. Barton. 2008. Red shirt colour is associated with long-term team success in English football. Journal of Sports Sciences. 26(6):577-582.

³ Hagemann et al. When the referee sees red, Psychological Science, Volume 19, Issue 8, Date: August 2008, Pages: 769-771

⁴ Joanna M. Setchell and E. Jean Wickings, Dominance, Status Signals and Coloration in Male Mandrills (2004), Ethology 111 (1): 25-50.