The present invention is drawn to an agent and process for altering the color of keratin fibers wherein the agent comprises: (A) a color base composition containing a fatty substance having a viscosity greater than about 50 mm2/s at 40° C., a rheology modifying polymer an alkalizing agent a one short alkyl chain hydroxy compound chosen from monoalcohols and polyols and an oxidative dye precursor and (B) an oxidizing composition comprising an oxidizing agent and wherein the pH of the agent for altering the color of keratin fibers is greater than 7.
