With WECOLOUR bleach, you light up your hair to up to six colour levels in one go if you choose 9% hydrogen peroxide. If you prefer the 6% hydrogen peroxide (which is milder), you can lighten your hair to a maximum of four colour levels. It does not matter whether your hair is undyed or dyed, but rather how dark your hair is. See also the FAQ "How much lighter can I go with WECOLOUR bleach?".