The present invention relates to a composition for dyeing keratin fibers, comprising, in a medium that is suitable for dyeing, a) at least one oxidation base and/or at least one direct dye, and b) at least one particular hydroxycarboxylic acid or a salt thereof. The invention also relates to a ready-to-use composition comprising the above-mentioned composition and an oxidizing agent. The invention also relates to a process for dyeing keratin fibers, in which a composition according to the invention and optionally an oxidizing composition, these compositions being mixed extemporaneously before use or applied successively, are applied to the said fibers; the composition(s) is(are) left on the fibers for a time that is sufficient to obtain the desired coloration; the fibers are rinsed to remove therefrom the composition according to the invention and optionally the oxidizing composition; the fibers are optionally washed, they are rinsed after each washing, and are optionally dried. Finally, the invention relates to a device for implementing the process.