It's an ice fog, something between hoar frost and soft rime. It makes weird ice crystals on everything. The fog is what's freezing, outside of it, it may not feel very cold. Roads look dry, not like black ice, they look normal at midday, but in the fog are actually covered with a sheet of ice. I spun out on what appeared to be an almost sunny morning, The thing I found particularly unnerving was the silence. It was eery, hard to describe; no wind, no distance sounds, like being in a bubble. Settlers called it White Death, since legend has it that inhaling the fog will freeze your lungs.
