I tried that salt bath on my old mouthpiece, left it in there for about 6-7 minutes and most of the tarnish had disappeared! There were little flakes that rose to the surface, and the water and foil turned a brown-black colour. I'm quite impressed!
However I think that a blue mouthpiece cup is rather cool, I'll be interested to see how the gold mouthpiece turns out. I'll see if I get a purple cup like whoever previously mentioned that! :)