What is the primary purpose of using a filler in hair coloring?

The primary purpose of using a filler in hair coloring is to provide an even base for color application. Fillers are substances that are applied to the hair to ensure that the color being used adheres well and results in a uniform shade. This is particularly important in situations where the hair has been previously colored or where there is a noticeable difference in porosity among different sections of the hair. This even base minimizes issues like blotchiness or uneven color absorption, allowing the final result to be more aesthetically pleasing and consistent across the entire head of hair.

While other choices may have some relevance in hair care, they do not align with the primary function of fillers in the context of hair color application. Enhancing fragrance, lightening hair color, or protecting against UV rays are specific to other hair care products or techniques, but do not primarily relate to the use of fillers in coloring processes.