I like the MIX of both the flat grey and the stone. Since they are similar, colorwise, it works fine. I do think your jewelry really pops on the plainer background. That said, since you do include that view in your set of listing pictures, I don't think there's any problem with spicing things up a bit and incorporating some pictures with the stone. Great work. I would be selective, however, about which items you use the stone with. As others have indicated, you don't want your item getting "lost" on the stone.
Other than the time sink of taking more pictures, making some changes to your shop can really feel great. I know. I've changed backgrounds several times over the past several years. I think it brings a freshness to your shop when you make changes such as you are suggesting.