Chuck -
Here is a picture of my friend's original 427 Cobra with undercar exhaust. He had this entire system made up out of Stainless Steel, and then polished. You can see it here, up on jack-stands, but, when the car is on the ground, it's hardly noticeable.
You could have your pieces powder-coated black, that should hold up. I believe Jet-Hot and Airborn Coatings both do black (nobody seems to want to do white - it's just not as durable as the black or silver finishes).
regards,
Jeff