Two-way categorization and cone contrasts of the color chips used in the World Color Survey (WCS).

A–B, I_wc as a function of R_LM and R_Y respectively. The sign of I_wc indicates the category that a chip was assigned to. The value of I_wc reflects the consistency of the categorization across the WCS database. R_LM and R_Y denote the L−M and (L+M)-S cone contrast, respectively. C, Scatter plot of R_LM versus R_Y. The chips in different categories are represented by symbols of different colors (red vs. black).