The black is most likely aniline dye mixed with shellac to make a black paint(ebonized as we say). If you want to be correct in the finish test the black with alcohol and see if it becomes tacky if it does then it is shellac, if not it is most likely varnish or lacquer. If it is shellac it can be blended if lacquer the whole will have to be painted. Lacqure does not blend well.