What is the function of a toner in hair coloring?

The function of a toner in hair coloring is primarily to adjust and enhance the final color of the hair. Toners are used after hair has been lightened or colored to refine the shade. They can help neutralize unwanted undertones, such as brassiness in blonde hair, and can add richness to the color or shift it to a more desirable tone, like cooler or warmer hues depending on the desired result. This adjustment process is crucial for achieving the perfect finish in hair coloring, ensuring that the final look combines both the base color and any tonal adjustments needed for a cohesive, polished appearance.