I also have an OBX 4-2-1 header. I can't tell if it's any louder because of the CAI. But I did notice it rev's a bit quicker from 4K and up. As far as heat and discoloration, the temp hasn't changed really...if anything it's cooler due to the fact that the steal does not retain heat as much as cast iron. Discoloration, shit if it bothers you buy a roll of header wrap, bout $40. + will cut down on the under-hood temp.
just my .02