I still don't know... I mean look at this:
I just did a 3x3 average eyedropper sample and scaled it up (used marquee and paint bucket) to show the shades next to each other. I don't think that's just weathering. Dirt and sand being kicked up on the underside is one thing, but a white dorsal surface? Doesn'd add up, as the debris wouldn't reach this area, especially not so uniformly.
In some cases salt water corroded some paint jobs pretty badly into a white color, but again it's only on the dorsal surface, and the belly, ventral tail, and engine cowling lack this (clearly, they are all much darker).
Fencer, what are the odds we're looking at a rather rare paint job? The quality of the photo isn't faded or bleached. It looks clear, but it's showing us very distinct discolorations. I'm of the mind that it's showing a fair representation of what the actual plane looked like.
I'm all for giving it a white shade on the upper dorsal surface! It looks like it fades to blue right around the canopy area.
EDIT: It looks like the same coat of paint on the belly between the landing gears. If you look at the top of the oil cooler intakes in the wing roots you see the same thing, but THERE it looks like paint has worn off to show a color underneath. Could it be that they covered the plain in ASW colors, or something, then painted it blue, or half blue? Or half blue then some of it wore off (on the wings)?