A novel process for dyeing human keratin fibers in the presence of an oxidizing agent, comprising applying to the fibers at least one anhydrous composition (A) comprising at least one fatty substance, at least one organic amine having a pKb less than 12 at 25° C., and at least one surfactant, at least one composition (B) comprising at least one oxidizing agent, and at least one composition (C) comprising at least one dye chosen from oxidation dyes and direct dyes; a multi-compartment device or kit, wherein at least one first compartment comprises the at least one anhydrous cosmetic composition (A), at least one second compartment comprises at least one composition (B), and at least one third compartment comprises at least one composition (C); and a ready-to-use composition for dyeing human keratin fibers, comprising at least 35% by weight of at least one fatty substance, at least one organic amine having a pKb less than 12 at 25° C., at least one surfactant, at least one dye chosen from oxidation dyes and direct dyes, and at least one oxidizing agent.