Process for treating hair, especially human hair, comprising the following steps: a- Hair is applied an aqueous composition obtained from mixing two compositions A and B wherein the composition A is an anhydrous composition comprising one or more persalts and one or more alkalizing agents, wherein the composition B is an aqueous composition comprising one or more oxidizing agents, preferably hydrogen peroxide and has a pH in the range of 1.5 to 5, wherein the mixed composition consisting of compositions A and B has an alkaline pH in the range from 8 to 11, b- left on the hair for a period of 1 to 45 min, c- rinsed off from hair and towel dried, d- Optionally the hair is dried, e- Hair is applied another aqueous composition obtained from mixing the two compositions C and B wherein the composition C is an aqueous composition comprising one or more hair dyes and one or more alkalizing agents and has an alkaline pH preferably in the range of 7.5 to 12, f- left on the hair for a period of 1 to 45 min, g- rinsed off from the hair, and h- hair is optionally washed with a cleansing composition and dried, Wherein the compositions in steps a and/or e are mixed with a composition D immediately before application onto hair for obtaining ready to use compositions, Wherein the composition D comprises i- one or more carboxylic acids and/or their salts having 3 or more carboxyl groups, and ii- one or more organic additional acids and/or their salts having one or two carboxyl groups wherein the Composition D comprises the acids and/or their salts i) and ii) at a total concentration of 10 to 100% by weight calculated to the total of Composition D, wherein the ready to use compositions have a pH in the range from 6.5 to 11 and comprise the acids and/or their salts at a total concentration in the range from 1 to 10% by weight calculated to the total of each of the ready to use compositions. a- Hair is applied an aqueous composition obtained from mixing two compositions A and B wherein the composition A is an anhydrous composition comprising one or more persalts and one or more alkalizing agents, wherein the composition B is an aqueous composition comprising one or more oxidizing agents, preferably hydrogen peroxide and has a pH in the range of 1.5 to 5, wherein the mixed composition consisting of compositions A and B has an alkaline pH in the range from 8 to 11, b- left on the hair for a period of 1 to 45 min, c- rinsed off from hair and towel dried, d- Optionally the hair is dried, e- Hair is applied another aqueous composition obtained from mixing the two compositions C and B wherein the composition C is an aqueous composition comprising one or more hair dyes and one or more alkalizing agents and has an alkaline pH preferably in the range of 7.5 to 12, f- left on the hair for a period of 1 to 45 min, g- rinsed off from the hair, and h- hair is optionally washed with a cleansing composition and dried, Wherein the compositions in steps a and/or e are mixed with a composition D immediately before application onto hair for obtaining ready to use compositions, i- one or more carboxylic acids and/or their salts having 3 or more carboxyl groups, and ii- one or more organic additional acids and/or their salts having one or two carboxyl groups wherein the Composition D comprises the acids and/or their salts i) and ii) at a total concentration of 10 to 100% by weight calculated to the total of Composition D, wherein the ready to use compositions have a pH in the range from 6.5 to 11 and comprise the acids and/or their salts at a total concentration in the range from 1 to 10% by weight calculated to the total of each of the ready to use compositions. wherein the Composition D comprises the acids and/or their salts i) and ii) at a total concentration of 10 to 100% by weight calculated to the total of Composition D, wherein the ready to use compositions have a pH in the range from 6.5 to 11 and comprise the acids and/or their salts at a total concentration in the range from 1 to 10% by weight calculated to the total of each of the ready to use compositions.