Question: when dying hair what developer to use?
Answer: For level on level coloring, use 10 Vol developer.
For 1-2 levels lift, use 20 Vol developer.
For 2-3 levels lift, use 30 Vol developer.
For 3 levels, use 40 Vol developer.
For most cases of pre-lightening with lightener, use either 20 or 30 Vol developer.