The pupil exhibits a response property somewhat analogous to perceptual red-green cancellation. Across a limited range of flash intensities near threshold, pupillary constrictions evoked by red flashes can be reduced, if not nulled, by the simultaneous addition of a green flash. The percentage of trials on which a stimulus-evoked response can be correctly discriminated from noise also falls to chance level as a green flash is added to the red flash. In terms of the quanta absorbed by L and M cones, the cancellation can be modelled as a function of [10.65*L-M].
Kimura, E., & Young, R. S. L. (1996). A chromatic-cancellation property of human pupillary responses. Vision Research, 36(11), 1543–1550. https://doi.org/10.1016/0042-6989(95)00229-4