Geometry of color perception. Part 2: perceived colors from real quantum states and Hering's rebit

Inspired by the work of Resnikoff, which is described if full details in the first part of this two-part paper, we give a quantum description of the space P of perceived colors. We show that P is the effect space of a rebit, a real quantum qubit, whose state space S is isometric to the hyperbolic Klein disk K. This chromatic state space of perceived colors can be represented as a Bloch disk of real dimension 2 that coincides with the Hering disk given by the color opponency mechanism. Attributes of perceived colors, hue and saturation, are defined in terms of Von Neumann entropy.