I have used Furniture Clinic. They do a colour match, sell kits, have videos. I currently have colour matched bottles for the Plus Four and a leather sofa we have.
The processes are similar to paint work. Applying the colourant is easy ( I use an airbrush or dab it on with a sponge). Fillers for deep marks, final sealant coat.
Craig's photos show how good it can be!
