The only hair color peroxide is able to remove is washable hair color that bonds to hair too long. Permanent hair color cannot be removed and is only lightened by the use of peroxide.
Porous and light-colored hair sometimes retains color from hair-coloring products that are advertised as "washable." Mixing one part of peroxide with one part of shampoo helps to remove the stubborn hair color. The mixture should be lathered and left on the hair for 3 to 5 minutes before rinsing. Peroxide lightens the natural hair color, so this technique should not be repeated too many times unless one desires significantly lighter hair.