What is the common purpose of a toner in hair coloring?

A toner serves a vital role in hair coloring, primarily aimed at neutralizing unwanted tones that may arise after the bleaching process. When hair is lightened, especially blonde or ash shades, it often can exhibit unwanted undertones such as yellow or brassy orange hues. The purpose of a toner is to adjust these colors, bringing them closer to the desired shade by cancelling out these undesired tones.

For instance, if the hair has a yellow undertone, a violet-based toner can be used, as violet is opposite yellow on the color wheel, effectively neutralizing and balancing the overall color. This process allows for a more polished and harmonious result, contributing significantly to achieving the desired final color of the hair.

While toners may add some shine and improve the overall appearance of the hair, their primary function is color correction rather than enhancing shine or creating volume. Thus, the focus on neutralization is what makes this the correct answer in the context of hair coloring.