Here is the link for my corrected P51D-20NA void.bmp file. The original void file has no delimitation of the wings, control surfaces, and fuselage. All was white around them. I used the path tool in photoshop to draw a line around those parts in an already skinned P51, then copy that path over the void image using a separate layer. Then I used the Stroke Path feature to draw the final lines. I then selected the area around, selected the void image layer, then filled the selection with black color, and voilà! I got a clear image that is easier to use for skinning. Hope you'll make good use of that new void file.
You should extract it to any of the P51 folders in <IL2 Sturmovik 1946 folder>\Paintschemes\skins\ of your game, since it should work with all of them