At one time, don't know if this is still the case, 586's could be purchased either in blue or nickel plated. Could it be that those "stainless" guns on gunbroker are actually nickel? Might be someone sees a silver colored gun in the photo and automatically assumes it's stainless.
BTW, I wanted to post my reply with a quote from the previous post, but couldn't quite figure out how to do it. I'm not very good at this computer stuff.