Permanent & Semi-Permanent Hair Color
Q: Can a permanent color be applied over a semi-permanent color? If so, how long do I need to wait before doing so? Can a semi-permanent color be applied over a permanent color?
You would want to be sure to take into consideration the base colors of the hair colors being used in order to prevent unwanted color results, but generally speaking, applying permanent haircolor over semi-permanent color should cause you no problems.
The reverse however, is not universally true. You can only apply a semi-permanent color over a permanent color if the semi-permanent color is darker than the permanent color. Permanent color formulas may contain hydrogen peroxide developer of a strength sufficient to actually lift the color of the hair to which it is being applied before the color is actually deposited.
Semi-permanent color never provides any lifting action to the hair and therefore cannot be used to lighten the hair whether the hair has been colored with permanent color or not.
The base color of your hair
The different types of hair coloring
How to color hair
Hair color levels and peroxide developer