It sounds like it's probably thinly plated (and not with a very high carat gold at that) and the plating is rubbing off. Gold tarnish is usually a darkish color rather than silver, and is more likely to happen with a low-carat gold. Maybe call BalNY and explain to them what's going on, and see what they advise in terms of cleaning. I'd worry about the Brasso as well, just because I'd be afraid that it might lift more of the gold. Alternatively, I'd go to the jeweler's, get some jewelry cleaner, and use that on a qtip to see if it works. Also, maybe try coating the non-tarnished ones thinly with clear nail polish, being very very careful, to stop them from tarnishing?