The only action of light on the pigment of cone vision, iodopsin, as on the rod pigment rhodopsin, is to isomerize its chromophore from 11-cis to all-trans. All further changes are “dark” consequences of this one light reaction. Although this reaction initiates bleaching, its immediate product is a more intense pigment. At low temperatures in the dark, this tends to revert to iodopsin rather than to bleach.