Jason looked up what happened to our rings yesterday and it is pretty interesting!
So, our rings are silver and the sulfur in the hot springs reacted with it, turning into 'silver sulfide,' if we had stayed in longer the colour would have moved past gold to brown to black. It is known as Black Sulphide.
To fix this, you can polish the rings, since it will normal silver below but that results in losing some of the material. Our plan is to reverse the reaction when we get home. If we put the rings with aluminium foil and baking soda than it will reduce the silver and silver Sulphide which will reform the silver metal.
There is not point doing anything about it now since we plan to visit more hot springs during the trip and exposing the rings to sulfur again. Even though Jason really doesn't like the bownish gold they are right now.
Part of the reason that gold is considered a more precious metal is that it is less reactive with other elements, so this wouldn't have happened if we hadn't gone with the cheapest material option like we did. But I love it, makes me like our silver rings even more!