99%, on the photos taken by my friend a difference between the grey areas ( which we know where they are ) and the questioned areas is more than visible and it looks to me pretty much like not painted metal.....look the intake rings on the engine which are painted, maybe the best photo to see the difference,and the corrosion stains looks like unpainted metal,I saw it in Szolnok on NMF Mig 19, these stains are most common on unpainted areas.....