I've heard that some trucks had the white on top from the factory (It's hard to find original photos of these trucks!) but perhaps not in that exact design.
This one looks more like a factory paint job & color, but I'm not certain.
I don't know if I like it as much as the earlier, full-top 2-tone, but it does add a nice bit of contrast.
If I decide to repaint mine, I may go with a 2-tone all the way to the roof, starting around where that first image I posted has it. It's an idea I'm tossing around. Plenty of time to decide -- I still have about a thousand hours of body work to do before I'm ready to mask & paint!