The difference between white magic and black magic is the intent to which the magic is used. Traditionally white magic is used for good intentions. For example, a karma cleanse or negative energy removal is always a white magic spell. No matter what the situation, this is always going to help the target. Black magic on the other hand is used in the form of breakup or love spells, were the outcome may not always be best for both parties. The is strong forms of black magic that deals directly with breaking and influencing someones free will. Everytime you cast a black magic spell there is bad karma created for you. It is always advised when casting black magic spells to either have a protection shield on, or to have your karma and energy levels immediately cleaned. The human body and mind operate much more efficiently in a clean pure karma and energy state.
Hope this clears up any questions about the two forms of magic!