The subject matter of the present disclosure is a method for the oxidative lightening and/or dyeing of keratinous fibers, more particularly of hair, whereina) a dye and/or lightening agent is applied to the keratinous fiber, said dye or lightening agent being obtained by mixing a composition (A), which contains at least one alkalizing agent, with a composition (B), which contains, in a cosmetic carrier, at least one oxidant,b) thereafter, within a period of one second to 24 hours after step a), a pre-treatment agent containing at least one salt of an isoalkylphosphoric acid ester, is applied to the keratinous fibers, more particularly the hair.
