Yes, the more I look at it, the more I think the flap inner surface is the same as the frame - bare metal.
BTW, my description of 'flat' meant a flat sheet, as opposed to stamped or formed, which, of course is fixed to the tapered, pressed frame. The 'flat' surface, angled and in the shade, is not 'capturing' the light as the frame is, but the tonal values are very similar, hence my thought that this part of the flap is also bare metal.
As for the top cowl panel and the wing root gun breech covers, I'm undecided - they could be 'weathered' bare metal, or they could be finished in a light-coloured primer.
I'm tempted to go for the latter, but close examination of the upper cowl, over the guns, reveals the flush rivets, immediately in front of the windscreen frame, which would suggest bare alloy. Also, the dirt and what appear to be hand / palm prints around the latches, also suggest bare metal, due to the way the dirt is 'spread' and its 'thin' appearance, more the type of staining one would see on dull, bare alloy panels, compared to the more 'ingrained' appearance that would be seen on a coated surface.
So with that in mind, I would agree with Andy, and suggest that both of these areas are oxidised, dirty, bare metal. Unless, of course, anodized alloy was used, as they certainly have the appearance of the dull grey, anodized alloy, which looks like the weathered, dull aluminium we're used to seeing on, for example, museum exhibits left in the open for many years.