[musclecar fan]

I've seen both "natural color" smog tubes and repro "black" smog tubes. What is correct? The check valves are raw metal, should the tubes be too? If they should infact be natural, has anyone tried removing the black coating on theh new ones or do I need to replate? Or, should they infact be black and the ones I've seen are old black colored ones where the paint burned off over the years?..... Thanks