When it comes to touching up the color on a black leather jacket, you can check out any of the leather garment cleaning services and see if they handle such work. Ram Leather Care is one. Price is a consideration here, as is quality of work. Or you can visit a shoe repair shop and pick up a spray can of black leather dye called Nu-Life (call first, as some businesses carry this type dye and some don't). When using this dye, treat your jacket and environment as you would when utilizing any color spray. Mask parts with masking tape that you don't want dyed, such as any snaps, and make sure to provide yourself an adequate breathing space.
Before applying any dye to the jacket surface, be sure to wipe away any dirt and grime build up with a moist towel on intended dyeing spots. Then with a paper bag, practice spraying the surface of the bag to get a feel of how much dye will spray out. The idea is to learn to spray the least amount of dye as possible. Very slight, quick spurts are best.
I found the best way to service a jacket with dye is to hang it from a wooden hanger in a position that gives you free access to front and back, like in the middle of the carport or basement. It's easier to work with, and if you plan spraying the whole jacket, it's the simplest way of coloring each section.
There's a solution called dye preparer made to remove the old dyes and polishes from footgear. You don't need this, as you're only touching up the existing color. And there are a number of liquid dyes available, but again you're only touching up.
Finally, and this step is optional, once you've touched up the jacket's color and let it dry for a day, you can add a coating of conditioner. There are many choices here. I like using Lexol and their terry cloth-covered sponge. Or you can simply apply a neutral-colored cream and buff with a soft cloth.
Some shoe repair shops will perform this service; just ask to see some of their completed work, be it shoes or a jacket. A quality-oriented shop will be glad to show off their expertise. The fall and winter seasons are the busiest, though, so be prepared for a longer turn-around time during this period.