My wife shoots a Cimarron (TTN) 1878 Coach Gun that's blued and I can tell you from first hand experience that the bluing on the receiver is very durable. As Abilene stated, it doesn't appear to have been polished at all before being blued. The frame is almost black. I don't mean to imply that the gun isn't a good gun. It is. The fit and finish is OK considering it's a Chinese gun, but it functions great. I didn't have to do anything to it to get it to function properly out of the box.
I shoot one that has a casehardened receiver. The casehardening is beautiful. It, too, functioned great out of the box.
I wouldn't hesitate to buy another one.