How to Lighten Coloured Hair
Rule #1
You cannot Lighten Hair that is currently Coloured with a Semi Permanent or Permanent Hair Colour that is Darker than the Colour you want to be.
For Example
Your Natural Colour
7 Medium Blonde
Your Current Colour
5.53 Chocolate Brown
The Colour you want to be
9.1 Light Ash Blonde
If you apply the Light Ash Blonde over your current Colour and Regrowth, you will end up with Light Ash Blonde Regrowth and Toned Chocolate Brown ends.