A method for treating hair comprising: A) carrying out the following sequence of steps: i) applying a first composition comprising one or more first cationic polymer(s) to a first portion of the hair; and ii) applying a second composition comprising one or more first anionic polymer(s) to a second portion of the hair; and A1) forming coloured layer(s) on the hair by applying a fourth composition comprising one or more second cationic polymer(s) to a fourth portion of the hair, wherein the second cationic polymer(s) are cationic coloured polymers; and B) removing the coloured layer(s) by means of applying a third composition having a pH of less than 7 to a third portion of hair, wherein the first, second and third portions have at least one first common area, and wherein the fourth portion of the hair has at least one common area with the first common area; wherein the first anionic polymer(s) are weak anionic polymers, wherein a weak anionic polymer is an anionic polymer whose charge is dependent on the pH when solubilized in water; wherein by cationic coloured polymer it is meant any cationic polymer(s) comprising at least one chromophore and/or at least one fluorophore either in the skeleton or as pendent group; wherein step A1) is carried out between steps A) and B. A) carrying out the following sequence of steps: i) applying a first composition comprising one or more first cationic polymer(s) to a first portion of the hair; and ii) applying a second composition comprising one or more first anionic polymer(s) to a second portion of the hair; and i) applying a first composition comprising one or more first cationic polymer(s) to a first portion of the hair; and ii) applying a second composition comprising one or more first anionic polymer(s) to a second portion of the hair; and A1) forming coloured layer(s) on the hair by applying a fourth composition comprising one or more second cationic polymer(s) to a fourth portion of the hair, wherein the second cationic polymer(s) are cationic coloured polymers; and B) removing the coloured layer(s) by means of applying a third composition having a pH of less than 7 to a third portion of hair, wherein the first, second and third portions have at least one first common area, and wherein the fourth portion of the hair has at least one common area with the first common area; wherein the first anionic polymer(s) are weak anionic polymers, wherein a weak anionic polymer is an anionic polymer whose charge is dependent on the pH when solubilized in water; wherein by cationic coloured polymer it is meant any cationic polymer(s) comprising at least one chromophore and/or at least one fluorophore either in the skeleton or as pendent group; wherein step A1) is carried out between steps A) and B. wherein the first, second and third portions have at least one first common area, and wherein the fourth portion of the hair has at least one common area with the first common area; wherein the first anionic polymer(s) are weak anionic polymers, wherein a weak anionic polymer is an anionic polymer whose charge is dependent on the pH when solubilized in water; wherein by cationic coloured polymer it is meant any cationic polymer(s) comprising at least one chromophore and/or at least one fluorophore either in the skeleton or as pendent group; wherein step A1) is carried out between steps A) and B.