My understanding was that the "understructure" (frame plus welded-on pieces) was painted as a unit. The door retainers would have been painted body color as they probably would have been attached to the understructure, as they couldn't have been added after the fenders and doors were attached, could they? Then the car would be built up with the wiring, engine, suspension. etc. Then the pre-painted body panels would be attached (with the fender beads attached to the fenders beforehand).
So, by my logic, body color.