I don't know what the original color would have been for the first heater in the link, but the second heater looks correct. The color and finish are spot on. You can get the same look with Hammerite Rustcap Bronze. It's as close a match as you're going to get. Click on my '53 GMC 1/2 ton link below and go to the second page. That's my heater after a Hammerite repaint. Matched the original paint perfect.
