Agents for dyeing keratin fibres, in particular human hair, wherein said agents are produced by mixing (A) one or more oxidation dye precursors in salt form and (B) one or more water-soluble salts of barium or of calcium, wherein the molar ratio (A)/(B), is between 1.0-1.4. Preferably, the oxidation dye precursors are in the form of sulfate salts and the calcium or barium salts are selected from barium hydroxide, barium chloride, barium carbonate, barium hydrogen carbonate, barium nitrate, barium bromide, barium acetate, calcium hydroxide, calcium chloride, calcium nitrate, calcium bromide or calcium acetate. Preferably the agent is in the form of an oil-in-water emulsion. Kits containing the agent and a peroxide developer composition are also disclosed. In an embodiment the dye precursor is p-toluene diamine sulfate and the salt is barium hydroxide. In another embodiment, a developer type dye is used in its salt from and this reacts in-situ with the barium or calcium salt to yield the free base form of the dye precursor and the exchange salt of the barium or calcium salt.
