How do you stop your gold jewelry turning your skin black?

If it is low carat gold (10 or so), the alloy metals might react to your skin. Anything but 24k will have some alloy in it, and jewelry is rarely made of 24k, since it is so soft. If you are highly sensitive to the alloys, even a small amount might cause a reaction. Furthermore, you sure your jewelry is really solid gold, and not plated? Plated jewelry will often react with the skin as you have described.