SUMMARYThe present invention is related to a process for colouring and straightening keratin fibres especially human hair in a single process. The novel process for colouring and straightening keratin fibres especially human hair according to the present invention includes the following steps:a- an aqueous oxidative colouring composition based on at least one oxidative dye precursor and optionally at least one coupling substance but not comprising any direct dye is mixed with a composition comprising at least one oxidizing agent and applied onto keratin fibres and rinsed off from hair with water after processing 5 to 45 min at a temperature of 20 to 45°C, optionally shampooed,b- towel dried,c- an aqueous composition comprising at least one reducing agent and having a viscosity of 5,000 mPa.s and more is applied onto keratin fibres and at the same time hair is attached onto a hard surface with the aid of the reducing composition in a straight form and rinsed off from hair with water after a processing time of 5 to 60 min at ambient temperature and towel dried,d- optionally hair is treated with a composition comprising at least one salt and/or at least one oil and/or oily compound and optionally rinsed off,e- optionally a composition comprising at least one oxidizing agent is applied onto hair processed for 2 to 15 min and optionally rinsed off from hair with water and optionally towel dried, andf- an aqueous oxidative colouring composition based on at least one oxidative dye precursor and optionally at least one coupling substance is mixed with a composition comprising at least one oxidizing agent and applied onto hair and rinsed off from hair with water after processing 5 to 45 min at a temperature of 20 to 45°C and towel dried and dried with a dryer or left to dry in the air.Further in step "c", hair can be combed through during processing of reducing agent or after processing of reducing agent is rinsed off from hair and hair is dried, hair can be straightened wit
