What effect does hydrogen peroxide have when used in hair coloring?

Hydrogen peroxide functions primarily as a developer and lightener in the hair coloring process. Its role is crucial in oxidation reactions, which occur during hair dye application. When hydrogen peroxide is mixed with certain hair color products, it helps to lift the natural pigment from the hair shaft, allowing the new color to penetrate more effectively.

As a developer, hydrogen peroxide opens the hair cuticle, enabling the hair dye to enter the hair shaft. It also facilitates the oxidation of the dye molecules, helping to form the desired color within the hair. This dual function of lightening the hair's existing pigment while developing the new color is fundamental to many hair coloring processes, especially in achieving lighter shades or going from darker to lighter hair colors.

The other options do not accurately describe the primary function of hydrogen peroxide in hair coloring. It does not act as a conditioner, does not add color by itself, and while it can contribute to color removal when used in high concentrations, its primary role in the context of hair coloring is as a developer and lightener.