yeah, those highlighting kits (colourlights- or whatever its called- the loreal stuff, im assuming is what you are referring to) wont strip out black dye pigments, you have to do that yourself first, and BELIEVE me, it is even a task with 40 vol. bleach sometimes.
removing black dye is a bitch. which is why (even though it look gorgeous) have stopped doing it. try using blondissima or similar bleaching kits on areas which you wish to hightlight first, than good old punky colour. if all else fails go to a good hairdresser. (or AXIS at john casablancas, it's cheap cuz students do it- THEY'RE WELL SUPERVISED- i promise) :) hope thats of some help... ?