Abstract
Arguments are put forward to explain the basic facts about colour vision in the frame work of a zone theory, a combination of the Young-Helmholtz and the Hering theory. Data on wavelength discrimination in particular as a function of luminance, necessitate to assume separate mechanics for red-green and for yellow-blue discrimination. Some psychophysical data on the other hand, like the Stiles-Crawford effects and those on chromatic adaptation, give reason to assume three different visual pigments in the receptors, of which the spectral absorption curves and the densities can be derived.