[Reference to the Abney effect within the scope of linear opponent-color theory]

The Abney effect states that desaturation of spectral colours does not only change their chromatic saturation but also their hue. By means of Hering's perceptual criteria "neither blue nor yellow" and "neither green nor red" and heterochromatic brightness matching, chromaticity loci were measured in a visual tri-stimulus colorimeter; the loci served for construction of an opponent-colour triangle and the associated opponent-colour space. The chromaticity line resulting from the perceptual criterion "neither green nor red" deviated markedly--as an expression of the Abney effect--from a straight line. This phenomenon was captured by piecewise linearizing. The transformation of the (known) fundamental colour space, which may be interpreted as a cone excitation space, onto the opponent colour space thus gained yielded an explicit opponent-colour theory that reproduces some aspects of the Abney effect.