Hi Szilard,

I'm pretty sure the sooty-grey wash is in fact caused by dirt.
The parts of the plumage most likely to get in contact with soot (in a charred tree, or in a chimney),are dark (face, breast and probably also crown and back),but not the underside of the wings, nor the basal parts of the feathers, which are clearly quite normal.

In all likeliness one would get dirty hands from holding such a bird:-)

Best regards
Peter