Used in hair dye formulations as a coupling agent to produce a range of permanent and semi-permanent hair colors. It reacts with other dye precursors, such as oxidative amines, to form larger colored compounds that remain in the hair shaft. Commonly found in commercial hair coloring products due to its ability to provide natural-looking shades and good color fastness. Also used in small amounts to adjust the hue and intensity of the final color. Requires alkaline conditions and an oxidizing agent, typically hydrogen peroxide, for activation during the dyeing process.