A packaging unit (kit of parts) comprising, packaged separately from one another, a) at least one container containing a cosmetic agent for changing the color of keratin fibers, comprising in a cosmetically acceptable carrier - at least one compound selected from the group of oxidation dye precursors, - at least one protein-siloxane polymer in a total amount of from 0.02 to 0.2 wt.%, based on the total weight of the cosmetic agent, containing at least one structural unit of formula and/or at least one structural unit of formula where R represents a protein hydrolyzate which is isolated from potato and comprises at least one NH2 group, X represents a *-CH 2 -CH -CH 2 -O-(CH 2) 3 -* group, R 1 and R 2 represent, independently of one another, a hydroxyl group, R 3 represents a hydrogen atom, n represents integers from 1 to 101, y represents integers from 0 to 1,000, preferably from 0 to 500, in particular from 0 to 100, and z represents integers from 1 to 1,000, preferably from 1 to 500, in particular from 1 to 100, wherein the hydrolyzed protein functional group R has an average molecular weight M w of from 295 Da to 26,000 Da, and b) at least one container, containing an oxidizing agent preparation which contains in a cosmetically acceptable carrier at least one oxidizing agent in a total amount of from 0.5 to 7.0 wt.%, based on the total weight of the oxidizing agent preparation, and at least one acid. a) at least one container containing a cosmetic agent for changing the color of keratin fibers, comprising in a cosmetically acceptable carrier - at least one compound selected from the group of oxidation dye precursors, - at least one protein-siloxane polymer in a total amount of from 0.02 to 0.2 wt.%, based on the total weight of the cosmetic agent, containing at least one structural unit of formula and/or at least one structural unit of formula where R represents a protein hydrolyzate which is isolated from potato and comprises at least one NH2 group, X represents a *-CH 2 -CH -CH 2 -O-(CH 2) 3 -* group, R 1 and R 2 represent, independently of one another, a hydroxyl group, R 3 represents a hydrogen atom, n represents integers from 1 to 101, y represents integers from 0 to 1,000, preferably from 0 to 500, in particular from 0 to 100, and z represents integers from 1 to 1,000, preferably from 1 to 500, in particular from 1 to 100, wherein the hydrolyzed protein functional group R has an average molecular weight M w of from 295 Da to 26,000 Da, and - at least one compound selected from the group of oxidation dye precursors, - at least one protein-siloxane polymer in a total amount of from 0.02 to 0.2 wt.%, based on the total weight of the cosmetic agent, containing at least one structural unit of formula and/or at least one structural unit of formula where R represents a protein hydrolyzate which is isolated from potato and comprises at least one NH2 group, X represents a *-CH 2 -CH -CH 2 -O-(CH 2) 3 -* group, R 1 and R 2 represent, independently of one another, a hydroxyl group, R 3 represents a hydrogen atom, n represents integers from 1 to 101, y represents integers from 0 to 1,000, preferably from 0 to 500, in particular from 0 to 100, and z represents integers from 1 to 1,000, preferably from 1 to 500, in particular from 1 to 100, wherein the hydrolyzed protein functional group R has an average molecular weight M w of from 295 Da to 26,000 Da, and R represents a protein hydrolyzate which is isolated from potato and comprises at least one NH2 group, X represents a *-CH 2 -CH -CH 2 -O-(CH 2) 3 -* group, R 1 and R 2 represent, independently of one another, a hydroxyl group, R 3 represents a hydrogen atom, n represents integers from 1 to 101, y represents integers from 0 to 1,000, preferably from 0 to 500, in particular from 0 to 100, and z represents integers from 1 to 1,000, preferably from 1 to 500, in particular from 1 to 100, wherein the hydrolyzed protein functional group R has an average molecular weight M w of from 295 Da to 26,000 Da, and b) at least one container, containing an oxidizing agent preparation which contains in a cosmetically acceptable carrier at least one oxidizing agent in a total amount of from 0.5 to 7.0 wt.%, based on the total weight of the oxidizing agent preparation, and at least one acid.