Colorimeter for the intuitive manipulation of hue and saturation and its role in the study of perceptual distortion.

A simple optical method for mixing coloured light is described. The observer has intuitive and approximately independent control over hue and saturation at constant brightness. The method facilitates colour matching by unpracticed observers. It allows children with reading difficulties to select a colour that reduces perceptual distortion of text. The chromaticity coordinates of this colour vary from one observer to another but can be very specific. Complementary colours can exacerbate the distortions and induce pain. For the majority of children reporting beneficial perceptual effects, the u' coordinate is less than 0.25.