A dye composition for dyeing human keratin fibres, such as hair, comprising at least one dissymmetrical polycationic direct dye of formula (I) below: Col1-Z-Col2  (I) wherein:Col1 and Col2, which differ in structure, are chosen from tazo dyes, methine dyes, azomethine dyes, phenothiazine dyes, triarylmethane dyes, xanthene dyes, phenanthridine dyes and phthalocyanin dyes andZ is chosen from linear and branched, saturated, unsaturated and cyclic C1–C20 hydrocarbon-based groups comprising at least one nitrogen atom and bearing at least one cationic charge; and also to processes for dyeing human keratin fibres using the composition, to the use of the at least one dissymmetrical polycationic direct dye of formula (I) as direct dyes, and to multi-compartment devices.