On most WW2 planes they used flush rivets. These are totally invisible on both painted and unpainted planes beyond a range of more than a couple of feet. As such, in the vast majority of cases, putting rivets on skins for WW2 planes is not only unrealistic, but a complete waste of time.
The only fasteners that are really visible even at very close combat range (where somebody else might notice them in the game, as opposed to you looking at the skin in ultra-close-up offline on the ground) are dome-head rivets and the big screws, dzus fasterners, etc. that hold down cowling, gunbay, and inspection/service panels. Domehead rivets protrude above the skin and thus either get scraped clean of paint in high traffic areas (IOW where people walk a lot) and thus appear as sliver dots, or collect grime around the edges in low traffic areas, and thus appear as dark spots (when you include their 3D shadow). The fasteners for removeable panels, however, had fasteners big enough for large scewdrivers to work on, were usually nowhere near flush, and thus were usually quite obvious from close AH combat range. These should always be darker than the surrounding skin (whether painter or unpainted) and, if in a painted area, should have some paint chips around them from the screwdrivers slipping off the fasteners.
