Todd, I spent many years when I worked as a glazier in and around the mills of Northwestern, IN. The times a new or refurbished hot metal car also known as a torpedo car were put in service, they were painted black. But certainly with all the heat burning off the paint, blowing dirt and dust, splashed pig iron from the blast furnace loading & unloading, they turned to mostly rust colored in a jiffy. As long as they were functioning properly, doing their intended job, until the brick inner liner needed relining, they remained in service. So I guess to answer your question, some weathered black and a generous amount of rust with a built up layer of iron splash & spillage around the opening would look quite appropriate. I put together 3 of them a while ago but have yet to paint and weather them accordingly. The main thing is they never look new once being delivered to the mill. Joe