I assume you are referring to the fresh air heater system.
I have seen several different shades & tones of hammertone paint on these old original heaters:
Greyish
Silverish
Root Beerish
I have even seen a few '54 heaters that originally had a goldish tint to them.
You can even find the aerosol hammertone paints at Home Depot & Ace Hardware.
If you do buy the non aerosol paint from J.C. just be aware that his paint requires the use of a catalyst or it will never dry.
I usually opt for the middle of the road hammertone shade when I restore these systems.
http://talk.classicparts.com/attachments/img_1189-jpg.22188/ .