Frozen fog also called "hoarfrost" in the Southern Appalachians is called "pogonip" by Native Americans out west. The beauty of "hoarfrost" is that it coats the trees with a thick covering of frost only where fog travels. In this image you can see the evidence of how selective this type of frost can be. The frost produces a very reflective surface which causes the coated trees in this image to appear blue as the trees reflect the deep blue sky above.
LynnFreeny.com