The GM camel color was a perfect match but I can't find it anywhere now. People suggested using Rustoleum's "aged copper" available at Home Depot - I tried it, it's close but not a good match so I broke down and bought the Universal bronse paint from Catalna Direct. Seems like good paint but shouldn't be 5 times the price.
Regarding paint flaking: I haven't had any problems with paint flaking off - make sure the surface is clean, I use denatured alcohol as a final wipe to remove any oils. When I repainted my heat exchanger, I stripped it and used primer. When touching up the engine, I don't use primer.