I had a client that used a color remover from Walmart to lighten her hair. When I colored over it, the hair immediately went black. What happened?

What happens to the hair when trying to color over the already color removed hair?

• Color Removers contain ingredients that reduce the color molecules and eliminate them from the hair. Not only do they damage the hair and make it very porous, but when color is applied over hair that has been lightened with color reducers, it is necessary to use a color 2 levels lighter than desired to avoid it becoming too dark.
• If your final color is a level 6, a level 8 color must be used and your final color result will be a level 6.