Indication for the Existence of at Least Four Basic Excitations in Color Vision

The tristimulus values of the spectrum colors are expressed as linear functions of four normal distributions which have wavelength as abscissa. This separation explains the main facts of dichromatism. It suggests a new color triangle. One of its vertices has a negative y-coordinate. Pairs of the center points of the normal distributions are collinear with this blue corner of the elementary color triangle. For convenience this triangle is transformed to the orthogonal and isoceles shape. Finally a tentative mathematical expression is given for describing the spectrum locus. The results are compared with the trichromatic coefficients of the CIE Standard Observer.