Dichroism

A colour which changes hue violently when the illuminant changes from say daylight to tungsten light is said to be dichroic. This happens with dyes rather than pigments which in general have less steep changes in reflectance. Som dyes which are green in daylight are quite distinctly brown in tungsten light and there are other similar colour changes to be found in certain dye classes. This phenomenon must not be confused with metamerism as this latter word only applies to a conditional match and for a match of course two colours are required.