Recently...
There was a "clean up" run. I know for a fact Stainless as I bought a few, I think there were blued ones too, but not sure.
Best thing to do is get the sn# we can get an idea of when it was produced and/or a call to Ruger will confirm a more exact date.
I have a blued fixed sight from the 1980's, it's a good shooter, I fit a Magnum cylinder and I find myself shooting the Magnum more often.