Quantitative judgments of color: The square root rule

Judgments of the appearance of colored papers blended with different proportions of white were obtained using a rotating color mixer. Responses consisted of a mark on a line labeled with the appropriate color name at one end and “white” at the other. Prior context was avoided by obtaining only single judgments. It was found for all six color displays that distance from the colored end of the line was proportional to the square root of the proportion of white present in the mixture. This square root relation is in keeping with the physical correlate theory and with other experiments involving gray papers, point sources, and luminous fields.