Since the 55 model year was a toss it out the door as fast as you can deal you can not use it as an example of what was done on later years either. I guess I should say every TF truck from 1957 to 1959 has had the frame painted black. These are the ones I have seen brand new as a youngster, and they all had painted black frames. No one would have bought a brand new chassis cab or flat bed truck in the day with the frame rusting. Everyone of them had nice black frames. I saw them.