I've found if I wear a camo ski mask (the full face mask kind) with my scentlok head cover under it there is very little visible fog from my breath even on the coldest days. The key is to cover up your nose and mouth so that you are breathing into some kind of fabric. It seems to dissipate it alot. Plus it keeps you warmer.

I put on the black one first, then the camo one on the outside. You can't see my breath or smell it for that matter.