The invention relates to an agent for colouring fibres (A). Said agent is produced by mixing two constituents (A1) and (A2), and is characterised in that the constituent (A1) contains at least one quinonimine derivative of formula (I), and the constituent (A2) contains at least one compound from the group consisting of aromatic amines and phenols. The invention also relates to a method for colouring keratin fibres using the inventive agent. ##STR00001##