The stone has to provide some sort of rejuvenation or healing because if not what is the purpose for Voldemort (who is just a spirit) to drink the Elixir. It would need to give him a body or something.
Back to the topic though i think different people view the terms for dark or black magic differently. I would classify dark as bad intent based spells or potions, and black with anything that shouldn't be meddled with. This being death, life,time, soul, and things of that nature.