I don't know that there's a hard and fast "ring rule," lol. But I get where you're coming from. I wear a wedding band but that's it, I don't really like wearing jewelry.
I would treat this like any other gift you receive from someone close to you, that you don't like. Which of course makes it difficult. In general it is very dangerous to spend a lot of money on a gift that is very personal to the gift giver's taste. Nothing you can do about that, he's gone and done it.
You could just not wear it, and see if he notices, though he may notice it, not say anything and just have hurt feelings. Or you could bring it up when you guys are talking about stuff and say, honey, I love you, but I feel really terrible that you bought this really expensive ring and it just isn't to my taste. Personally, that's what I would do - maybe you can still return it if it's pretty new. Or you could wear it for a while and just taper off - or if you REALLY want to avoid conflict, "lose" it or let it be "stolen." Not that I recommend that.