I think he's being sarcastic?
I liked it with the dark engine hatches more than the lighter grey ones. But maybe that's just because a lot of the old locamotives were painted black, maroon or dark green, so it feels more natural that way.
But i geuss it's not really worth commenting on colour theory when the whole thing isn't finished yet.
I'm not sure if the light gray that forms most of the train works well with the bright orange...try desaturating the orange a bit, see how that looks.
EDIT: so you didn't use a normal map?