I used this stuff in black, holdes up very well so far (about 1 year) http://www.caswellplating.com/aids/techline/index.html#exhaust doens't come in white, but aluminum and titanium.
I got white VHT header paint at Summit. Good for 1100 degrees. Make sre you use the VHT primer first.
I got mine from advance auto parts. if you don't have one in your town I think Eastwood sells it mailorder
Ah, memories.....headers painted with white VHT with greasy handprints all over them from constantly working on the engine.