I have been around lots of TF trucks. I have seen under them when brand new, yeah I was just a kid, the frames were painted black. I am now wire brushing a never touched frame I'm 3rd owner, it has black paint. For any TF owners to verify the frame color, on an untouched frame, just remove the front bumper brackets from the frame, you will find the best example of what color it was there.
What I'm not sure was painted or not is the front spring rear brackets that are riveted on the frame, the frame may have been painted before they were added. Gosh there should be factory photos showing the frames???