Zone theories of color vision transform cone sensitivities
to channel sensitivities before transmitting these signals to the
brain. The concepts of “unique hue” and “color
opponency” are fundamental to an understanding of this
transformation. Saunders & van Brakel question the objectivity
of these concepts. Statements in their target article indicate that
the reason for this questioning stems from a failure to appreciate the
constraints inherent in the definitions of these concepts.