Black - oils for diesel engines; white - oils for gasoline engines.
Since the application ranges of seasonal oils of adjacent SAE classes overlap, short-term temperature changes can be ignored. It is permissible to mix oils of different viscosity classes if oil topping up is required and the ambient temperature no longer corresponds to the viscosity class of the oil poured into the engine.
Additives, no matter what type, should not be mixed into either oil or fuel.