Ocular filtering of ultraviolet radiation and the spectral spacing of photoreceptors benefit Von Kries colour constancy.

Ocular filters in the eyes of many vertebrates, including humans, absorb wavelengths shorter than approximately 400nm. These filters prevent the beta-band of a visual pigment from being exposed to ultraviolet radiation, essentially narrowing the spectral sensitivity of the different photoreceptor classes. A comparison of different hypothetical visual systems is used to show that von Kries colour constancy is improved by ocular filtration of ultraviolet radiation, whilst there is no reduction in colour discrimination. Furthermore, it is shown that the asymmetric spectral spacing of different photoreceptor classes present in the human visual system may benefit colour constancy. The results are interpreted in relation to predictions of von Kries colour constancy for a standard human observer.