Red can symbolize danger, heat and even anger.
It's true: The color's appearance in road signs, stoplights, labels and flushed cheeks often cautions humans to avoid harm.
One study even found that Olympic competitors donning red uniforms were more successful at winning events, suggesting the color intimidates the competition.
And a recent set of experiments featured in the journal Psychological Science indicates humans' apprehension of red may have evolutionary roots, leading to greater consideration of the color's use in human sports and primate habitats.
In the study, Dartmouth College researchers measured reactions from rhesus macaque monkeys when they were given the option to take food from human testers. The species was studied because these primates have similar visual capabilities as humans and use redness as an expressive form of communication - just like people blush or redden when aroused or angry.
Scientists set up several experiments allowing the monkeys to "steal" food from human testers, each of whom dressed in a different color T-shirt and baseball cap - either red, green or blue. Researchers predicted the monkeys would avoid stealing from the tester wearing red, and they were right.