Really, really far back in time, we are now talking about ancient history. There was a people, called the Negro Sapiens, they ruled the underworld with the master Lucifer, other known as Gary Coleman. The Negro Sapiens practised magic every day, and extinguished all of white magic in the white heaven using their gipsy powers.
So long story short: Black Magic = Magic performed by Negro Sapiens ( no longer exists ) White Magic = Magic performed by white sorceress ( no longer exists either )
In video games white magic is focused on healing and restoration. It can be used for fighting but only by those who are holy or have good intentions and pure hearts. Black magic forcuses more on damaging things and can be used by anyone though it often involves sacrifice or corruption.
Opinions. Magick is magick. It's up to to the witch himself/herself to decide. I don't categorize it either way. But to answer your question, white magick is used for protection and things that could never hurt anyone. Black magick is used to hurt or manipulate someone.