The invention relates to the dyeing of keratin materials using phenylpyrido[1,2-a]indolinium-derived thiol and disulfide fluorescent dyes. The invention relates to a dye composition comprising a phenylpyrido[1,2-a]indolinium-derived-chromophore thiol or disulfide dye and to a dyeing process with a lightening effect on keratin materials, in particular keratin fibers, especially human keratin fibers, such as the hair, using said composition. It similarly relates to novel phenylpyrido[1,2-a]indolinium-derived-chromophore thiol dyes and to the uses thereof in lightening keratin materials. This composition makes it possible to obtain a coloring with a lightening effect which is particularly resistant and visible on dark keratin fibers.