The present invention relates to a process for colouring hair keratin fibers, in particular the hair, comprising the application of a composition A and a composition B to said hair keratin fibers, in which: composition A comprises at least one (poly)carbodiimide compound, and composition B comprises: at least one associative polymer; and at least one compound, different from the associative polymers, containing at least one carboxylic acid group; at least one compound, preferably at least two compounds, containing at least one hydroxyl function; composition A and/or composition B comprising at least one colouring agent chosen from pigments, direct dyes and mixtures thereof; and in which composition A and composition B are applied simultaneously or sequentially to the hair keratin fibers. The present invention also relates to a device for colouring hair keratin fibers.