Fig. 1. Comparison of different indices of dichromatism. Geometric mean regression of colour discriminability and segment classification scores against principal component analysis (PCA) scores. Colour discriminability, segment classification and PCA dichromatism scores were calculated using spectrophotometer data. Scores for each index were standardized to a mean of zero and a standard deviation of one. (A) The solid line indicates the regression line of the segment classification scores (b=0.71±0.02) against the PCA scores. (B) The solid line indicates the regression line of the colour discriminability (b=0.70±0.02) scores against the PCA scores.