I have a mother's ring that is 10k gold and am having the same problem with it turning my finger black. At times it will also turn the neigboring fingers where it rubs. I also noticed that oen of my earings (after a few months low carbing I got both my ears pierced 3 tiems) was tarnishing green. I just associated it with my natural chemistry as prior to LC I didn't really ever wear jewlery, esp not higher quality.