Black: Ruled by Saturn. Black has long been considered a negative color which is used strictly in black magick; this is a misconception. This color is used in a variety of ways. E.g. of uses: Includes banishings, curses, hexes, binding, domination, commanding, controlling, etc. Retributive spells (used only under extreme circumstances such as violent crimes, i.e., murder, rape etc.) would call for a Justice seal while asking that the associated karma be balanced out. Black candles also help with grounding oneself and are great for protection when lit on a Saturday (Saturn’s day).
Of course common sense says in general DO NOT LEAVE A CANDLE BURNING UNATTENDED IN AN UNSAFE MANNER. SUGGESTION PLACE CANDLE IN A BOWL OF WATER OR SNUFF OUT WHEN LEAVING YOUR HOME.