I will introduce high light coloring technique.
First, we'll talk about gray hair. When it comes to gray hair, the highlighting technique will have a different effect from full touch up for gray hair. For full touch up, when the gray hair (roots) grows out, it will be very obvious. The gray roots and the previously dyed black hair will have a high contrast. Whereas, if the highlighting technique is used to cover up the gray hair, the gray hair will be less obvious when it grows out. The highlighted areas will be brighter, hence, the gray hair will be able to camouflage.