Scotopic vision in colour-blinds.

Alleles causing colour-blindness are present in humans at non-negligible levels, and it is not yet understood how colour-blindness is maintained, since colour-vision probably provides a selective advantage, e.g. when foraging. We show that after dark-adaptation colour-blinds had lower light perception thresholds than colour-normals (0.44 log-units), which may give a selective advantage under scotopic conditions, which may offset the disadvantage that colour-blinds suffer during foraging.