Its pretty easy I have very dark brown hair and I recently dyed my hair red it turned out pretty good and bright the best part I just used a box dye from the store I didn't get it profesonaly done :)so it was cheap I don't know if I would work for black hair I'm not sure wich one you have but it worked for me hope this helped :D

What brand did you use? Was your hair dyed before, or was it naturally dark?