AbstractWe examined the effects of spatial frequency and colorimetric purity using a hue‐matching technique. At constant retinal illuminance, hue matches of alternate stripes of square‐wave gratings changed with spatial frequency. At high spatial frequencies the data did not tend towards tritanopic confusion loci. Several alternative hypotheses, including optical factors, chromatic induction, and changes in the relative sensitivity of the opponent‐colors channels, are discussed. None of these mechanisms can explain all of the