I have a 620 and my exhaust never turned blue. I thought only the shinny pipes turned blue. I dunno if it's chrome or what but I thought it was only shinny metal that turned blue when heated. Mine turned a bronze-ish, light brownish color, but I cleaned them with a metal polish and they look good. Not perfect like new but shinny and good. By the way, I am talking about the piping, not the mufflers.