What appears white in the painting is where the de-icer boots were removed. You tend to see three variations with the de-icer boots and OD/Gray birds.
1-de-icer boots on, meaning the black rubber is there
2--de-icer boots off leaving the bare metal showing (most common)
3-de-icer boots off and OD camo painted over it. I have seen one 91st BG example, "Miami Clipper" that had the BMF area painted yellow, but that's the only example I've seen of another color painted on it.
Clearly the 100th bird you are working on, had the de-icer boots removed at some point.