Maybe you have a pair of black shoes that you think would look great in red or a black leather ottoman that you wish matched an oxblood-coloured chair. Or you have a scuffed black leather jacket, and you want to renew it to its original pigment. You can do all of those things if the leather has a surface coat of acrylic leather paint (called dye in the leather field). This accounts for almost all leather goods, including shoes, car and furniture upholstery and leather clothing. Recoloring leather is much like repainting an automobile; you must prepare the surface, then give it an even spray of its new (or restored) colour.
Choose an interim colour if you are recoloring a black leather item to another colour. This interim colour acts as a coat of primer and obscures the black. For example, use yellow before green, light blue before dark blue and pink before red. Skip this step if you are restoring a black item.
Tape off anything you do not wish to paint; for example, hardware on a purse, the rubber soles and heels on a pair of shoes, the legs on a chair or the zipper on a jacket.
Remove any surface waxes, oils or conditioners; these will keep the paint from adhering to the surface. Use a leather preparing product like Fiebing's deglazer or Meltonian's Nu-Life Color Preparer. These contain organic solvents, which both remove the finishes and penetrate the leather to help it accept dye.
Spray the item lightly with your undercoat. Allow to dry per manufacturer's instructions, perhaps 20 minutes. Repeat once. Most of the black should be obscured.
Allow the undercoat to dry thoroughly, overnight, to ensure that it does not mix with your new top coat to create a third (undesired) colour.
Spray the item lightly with your finish colour and allow to dry per manufacturer's instructions.
Repeat up to three times, then allow the item to dry overnight before using.
Spray lightly; a lighter coat will not give you the coverage you desire, but it will not drip or run, either. Be patient. Two coats should restore a black item that you are not recoloring. You may order leather dyes and complete recoloring kits, but, shoe repair shops typically sell both the deglazers and a variety of acrylic leather paints. You may use a small paint gun---the kind you'll find in a hardware store---instead of buying acrylic dyes in a spray can (not all colours are readily available in spray cans).