U.S. Patent No. 7,429,276 B2
KPSS-Kao Professional Salon Services GmbH, Darmstadt (Germany) has patented a process for coloring hair. The patent covers a composition comprised of at least one oxidation dye precursor and at least one acidic direct dye selected from acid red 52, acid violet 2, acid orange 4, acid red 27 and acid yellow 10, with the condition that it does not comprise cationic direct dye. That composition is then mixed with hydrogen peroxide. That mixture, which has a pH between 6.8-12, is applied to hair for 15-45 minutes at ambient temperature or a temperature between 30-45°C.