It depends on which heater you have. There were three types used in the Henry J (4 if you count the very early ones, some of which used the 1947/48 Kaiser "Air Conditioner" heater.)
The most common one is this one, all of which were metallic gray
Some '51s and a lot of '52s I've seen were equipped with left-over '49/'50 Kaiser heaters, which were metallic tan, maybe there were other colors but I've never seen one:
Then there's this one,
which I've seen in metallic gray and metallic tan but I don't know if the tan ones were original or not. Actually, the one pictured looks like it's been painted or it's very nice NOS.