Mine was kind of weird and I have never determined if it was 'factory painted' or not, but in case it matters: It had a grey color painted on it that perfectly matched the interior original paint (that was protected from later changes by being mostly inaccessible). It was hand-painted, and was applied on even the fuel line part that was accessible in the cab without the seat in place. The backside of the tank was bare steel.

It looked like the factory (or someone shortly thereafter) installed the tank, then hand-painted it to match the interior color.

Can PM you some pics if that helps.

-Jim


1957 Chevrolet 3100 Stepside
235, 3-speed w/OD
In the Stovebolt Gallery