Color and Categorical Claims

The effect of color on psychological functioning is the topic of a large literature. Published claims include that viewing blue causes calmness and that viewing red decreases test achievement. However, almost all these claims are made on the basis of testing just a single, or sometimes a few, hues. But colors like red are categories that comprise many perceptually distinct hues. Making a general claim about red on the basis of testing just one or two red hues may be akin to testing the reliability of one Toyota car and one Tesla car, finding that the Toyota is more reliable, and concluding that Toyotas are more reliable. This methodological issue was omitted from a recent literature review that was otherwise rather comprehensive. This article provides arguments for why this is a major issue and suggests ways to address it.