The present disclosure relates to a novel dye composition for the dyeing and/or lightening of keratin materials, such dye comprising a hemicyanin styryl chromophore thiol or disulfide dye of formula (I) or (II): the organic or mineral acid salts thereof, optical isomers and geometric isomers thereof, and the solvates thereof such as hydrates. The present disclosure further relates to a dyeing process with a lightening effect on keratin materials, in particular keratin fibers, including human keratin fibers such as the hair, using said composition. This composition makes it possible to obtain a coloring with a lightening effect which is particularly resistant and visible on dark keratin fibers.