Disclosed herein is a dye composition for dyeing human keratin fibers, such as the hair, comprising a direct polycationic dye of formula (I) below: Col-Z-Col  (I) in which Col, which may be identical or different, is a monocationic dye chosen from azo dyes, methine dyes, azomethine dyes, and phenothiazine dyes; and Z is chosen from linear and branched, saturated and unsaturated C1–C20 hydrocarbon-based groups comprising at least one nitrogen atom and bearing at least two cationic charges, and also to processes for dyeing human keratin fibers using said composition, to the use of the dyes of formula (I) as direct dyes, and to multi-compartment devices.