Can the negative afterimage appear only if there is light or is it possible in darkness?
Glutamate release from photoreceptors is inhibited by incident photons (ref). During photobleaching, assume that the effect of an incident photon drops to zero. The implication then is that if all light is removed subsequent to selective photobleaching, there will be no difference in activation between bleached photoreceptors and unbleached photoreceptors. This observation suggests that no afterimage will be visible in darkness.

But there might be rebound effects or other effects of light adaptation that will result in a perceivable afterimage in darkness. Certainly there are hallucinatory visual patterns than can be generated cortically, suggesting that a cortical afterimage could be generated in darkness.