Colors are constructs of the brain, not physical realities, and the presumption would thus be that whatever color or color combination is most appealing to humans is attractive because of some ecological/evolutionary advantage. The National Fire Protection Association uses color-coded warnings in which red indicates flammability, and yellow indicates reactivity. The U.S. Department of Transportation identifies the Pantone colors for its traffic signs, reserving red , yellow , and orange for the most important cautionary signs. So do we instinctively associate danger with these colors? After all, Mother Nature warns us with the red and yellow of the poisonous coral snake . If not by instinct, then perhaps by experience we learn to associate danger with red and yellow.