I have vague memories of reading about the coating on F-117. It was supposed to be multiple layers of epoxy paint with suspended ferrous particles, each layer cured under a different magnetic field to align them. To re-coat, the plane would have to be disassembled. The effect they wanted is most likely cancellation, analogous to anti-reflective coatings on glass. Idk.

Furthermore, I have seen pictures of F22 with brown rust stains on panels that should not have any steel in them.