both, color doesn't make a difference. The chrome can't go as high because the chrome is really aluminum particles, that is why when sprayed it looks really rough and you need a special vibratory tumbler to polish it and it won't take 2000, the reason they don't give color options at that temp, they would all discolor badly, even the black can lighten to a charcoal. I have coated the inside of the housing and had no tolerance issues and it should spool slightly faster because the edge gap has been decreased (I've done a few, but they are all different, your mileage may vary.) Don't spray heavy and don't get runs on the inside. The general idea has been said, ceramic keeps the heat in and flowing out verses radiating out to other parts and helping clear the exhaust chamber at high rpms. Jet-Hot is a company name they do ceramic coating and use the same as everyone else. There's only 2 places in the US that make the ceramic and both lines are almost identical. Let me know what they quote you. 8)