Abstract
This chapter focuses on the incompatibility of afterimage colors. Several quasilogical, semantic, and metaphysical questions having to do with incompatibility come up in color theory, and the problem is so complicated and fragile that it is argued here that, despite some marvelous work on the topic, the problem remains to be sorted out. Every naive subject who encounters afterimages without prejudice has agreed that they have color; this is mentioned here because it is the initial and also the commonsense view. However, accepting that a physical account of color incompatibility is right for physical colors makes an account for the incompatibility of afterimage colors improbable. One can provide a physiological account based on opponent processes, but this will deliver only a contingent truth or a necessity relative only to a particular retinal structure and postretinal neural coding.