Thank you. I was bird-sitting him and just got curious what he'd be called.
I don't have more pics of him; he was picked up this am.
When I looked at his markings last nite, I had a difficult time telling if they were grey or brownish.
Looks like a full body greywing with a dark factor to me, but sadly we can't see all of his wing feathers because he is clipped. I would advice you to let them grow out, not in consideration of finding out what mutation he is, but to let him live as the bird he is.