The present invention relates to a process for oxidative coloring keratin fibers especially human hair wherein dyeing composition comprises a cross linked copolymer. The objective of the present invention is a process for oxidative coloring hair wherein compositions A and B are mixed, composition A comprises at least one oxidative dye precursor and optionally at least one coupling agent and optionally at least one direct dye in a cosmetically acceptable medium and composition B comprises at least one oxidizing agent in a cosmetically acceptable medium, and applied onto hair and processed for 1 to 45 min at a temperature range of 20 to 45°C and rinsed off from hair, wherein at least one of the two compositions A and B comprises a cross linked copolymer of vinylpyrrolidone, vinylimidazol, 3-methyl-1-vinylimidazolium and methacrylic acid.
