At work we got some large (50 lb.) nickel plated steel parts. People who handled them, while wearing gold jewelery, had their skin turn black, where the jewelery was. It wasn’t dark black, more like someone had rubbed pencil shavings on them.
So where did the black come from?
This shouldn’t happen with pure (24kt) gold jewellery - but for items made of 14kt gold, the other metals in the alloy (which may be any/all of copper, silver or even nickel) can react.
When you touch two different metals together, you’re effectively creating a galvanic battery - like you can do with pieces of zinc and copper pushed into a lemon - except it’s nickel and alloyed metals in the gold, plus the sweat on your skin. The same chemical reactions that create a small electric current also result in compounds of the metals (maybe silver oxide in your case)