Use of a product for keratin fibers, containing at least one specific polymer combination for improving the color retention of oxidative hair colorations

Method for treating keratin-containing fibers, in particular human hair, comprising the following steps:

• i) carrying out oxidative dyeing of the keratin-containing fiber,
• ii) applying an agent to the oxidatively dyed keratin-containing fiber, said agent including a cosmetically acceptable carrier and
• a) at least one copolymer A comprising at least one structural unit (A1), at least one structural unit (A2), at least one structural unit (A3), and at least one structural unit (A4)
• wherein
• R1 stands for an optionally heterofunctionalized alkyl radical;
• R2 stands for an optionally heterofunctionalized alkyl radical which is different from R1;
• R3 independently stands for an optionally heterofunctionalized alkyl radical which is different from R1 and R2;
• b) at least one copolymer B, which is different from copolymer A, having at least one structural unit (B1)
• wherein R4 stands for an optionally heterofunctionalized alkyl radical.