I'm a beautician and my first opinion is to see a professional! If you don't have experience with doing a bleach service and a tint back one you may have another problem in the making. The blonde area, depending on how light it is can get some very masty color casts by putting a too dark color over it without a filler. Again trying to bleach out or color remove the black can also give unwanted results. It has to be watched very closely or there can be damage to the hair. A demi color would be the best choice on the blonde..it is a deposit only and use one shade lighter than the desired results. But now maybe you have started a new trend..lol. JMHO