They don’t always change the stem when they tighten the diamonds.

If they did, they should have told you that they had done so.

All I can say is that the the stem should not be turning dark on you if it’s made out of white gold. Others can feel free to correct me if I’m wrong, but usually only silver and plated jewelry turns dark like that.

You should take it in to another fine jewelry shop and ask them to determine what’s wrong with the metal.

I agree generally with the previous post with one caviat… Have you changed your diet recently maybe you have begun eating more citrus? There are a few diet changes can affect Gold jewelry, I know that in the summer when I tend to drink alot of Orange juice my bracelet which i wear often will turn by skin dark and also gets a dark film on it. Same with my Diamond Earrings.

So taking them to another jewelry and having them cleaned is a good idea, I just can’t see the benefit from the original jewelry changing out your earrings without telling you.