Acetone helps dull and remove any protective finishes. It also takes the dye out of the leather – but your results will depend on the quality and method of the dying. If your leather is black all the way through, acetone will probably not do much because of the amount of dye. Ideally, you want the acetone to reveal some of the brown leather on areas that normally have wear (seams, elbows, edges, etc). This may take a lot of acetone and some time and energy.
One of the side effects of washing your garment is that it may remove some of the dye from the leather.