Some people seem to think gold plating on a mouthpiece will darken the sound but I don't think so. The gold is actually a little softer on the lips but it is subtle. I'm not sure I could pick out the difference blind. I didn't find much tonal difference at all when using the Yamaha GP series pieces(when compared with identical standard models) and I think the differences I did experience were more related to weight than plating.
To be honest, I think what plating you choose on your mouthpiece is best determined by how well it will match your horn. Get gold for lacquer and silver for silver!
