Ring fingers (actually, any fingers or thumbs that are adorned with rings) can turn funny shades of blue when metal combines with the oils in your skin.
This hack is an oldie but goodie: use clear nail polish on the inside of your rings to keep the metal from discoloring your fingers. Start with a clean ring, and add a few layers of clear polish, letting it dry between layers.
Of course, if your rings are made of 14K gold or platinum, you can skip this step. But remember: good things come in small packages–even if they aren’t 14K!