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 from about 50% to about 80% by weight of a fatty substance comprising a high viscosity fatty substance and optionally, an additional fatty substance a rheology-modifying polymer an alkalizing agent a 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.
