In hair coloring, what is the purpose of a toner?

A toner is specifically designed to neutralize unwanted undertones in colored hair. When hair is lightened or colored, it often develops unwanted tones, such as brassiness (orange or yellow hues) or dullness. Toners contain various pigments that can counteract these undesirable tones by adding a complementary shade. For instance, a purple toner can neutralize yellow tones, while a blue toner can address orange tones. This process is essential for achieving a more balanced and aesthetically pleasing hair color.

The other choices do not align with the primary function of a toner. Changing the hair's structure relates to chemical processes like perming or relaxing, while lightening hair involves the use of bleach or lightening agents. Adding volume typically refers to styling products rather than coloring techniques. Thus, the role of a toner in hair coloring is specifically to refine and perfect the hue by addressing any unwanted undertones.