Here's a picture of an un-restored, low mileage 1949 GMC 1/2 ton long bed truck that shows the fender bolts unpainted and the side angle strips body color.
'49 bed The bed itself had been repainted so it is difficult to tell what the actual color of the bolt heads were.
On the bed bolts, I have spoken with Jim Gebhardt, who is the VP with the national VCCA and judges for them and also owns a shop here in the Atlanta area selling classic cars and trucks. I took my recently completed '52 GMC (on which I had tried to do a "factory correct" restoration) by his shop for him to see and one of his comments was the bed bolt heads that secure the strips should be painted black. I believe he also told me that the ones actually securing the bed to the frame would have been unpainted. I do want to get a copy of the VCCA judging standards and review them before I paint the bolt heads - just to be sure.
Mike