A well-worn motorcycle jacket will show some wear over time. Most jackets are not dyed, but have a surface coat of paint and some finish. This type of finish shows lighter through its scratches and is more prone to fading than a deep dye. You can restore the colour with the durable, acrylic-based paints available for restoring shoes. You may find these materials through leather retailers, shoe-care providers or cobblers.
Wipe off any dirt or grime with a clean, wet cloth. You do not need detergents or saddle soap.
Prepare the surface using a leather deglazer. This removes waxes, oils and finishes, preparing the leather to receive the paint. Fiebing deglazer is available from leather retailers. Meltonian's Nu-Life Colour Preparer performs the same function (and, Meltonian offers leather paint as well).
Select a well-ventilated area to paint the jacket, but one in which no dust or debris will fall onto the jacket when it is wet with paint.
Hang the jacket on a heavy hanger, over several sweaters or sweatshirts or other heavy items, and with those items encased in a bin bag. This will "plump up" the jacket, ensuring that you reach every centimetre and wrinkle.
Push a broomstick through the sleeves, into one sleeve and out the other. Stuff the sleeves with socks or some other object, to plump the sleeves and open up the leather.
Spray the jacket lightly, from top to bottom, with a paint colour that matches the jacket closely. Do not paint more heavily over the faded areas; you will even the colour with a second or third coat.
Wait 15 minutes for the first coat to dry. Repeat the spray, no more than twice.
Allow the jacket to dry for at least two hours.
Finish the coat with a high-quality conditioner, like Lexol or Fiebing's. A spray conditioner is likely the best choice, as it will have a lower oil content. A conditioner heavy in mink or neat's-foot oil will soak through the paint, and may loosen it; a spray conditioner will protect the paint's surface.
Leather World Technologies offers all-in-one leather recolouring kits; while these are supposedly for leather upholstery, upholstery paint is very durable, and will work well on your motorcycle jacket. Angelus Acrylic Leather Paint No. 720 is very durable, and popular among leather artists, but does not come in a spray variety. You can use this water-based paint with a paint sprayer, which are available from most hardware stores. Spray your jacket every few weeks with the conditioner, to protect it from UV rays and protect the surface paint. If the scratches and worn spots of your jacket retain their colour, then, your jacket is aniline dyed. You must dye, rather than paint it.