My heavy two piece suite for cold weather is Advantage camo. So once the snow falls I use a light white cover jacket that I got from Cabela's to go over my regular suite or Carharts. It was relatively inexpensive. If I am in heavy trees I remove the white top easily, so I blend in with the trees, and don't stand out. I don't worry about my pants since they look like a bush under me if I am standing. If I am sitting they are covered by snow anyway.
But a white poncho could easily be made by cutting a hole in an old sheet. Just make sure it is not too long to trip on, about the knees usually works well. (Make sure you discuss this with the lady of the house first) Wrap a white belt around yourself, or install some snaps under the arms and on the sides, to hold it closed, and wear a white stocking hat and face cover. White gloves and white tape on the gun would complete a good snow camo outfit.
If it is snowing I sometimes carry an old white blanket. Once I am sitting and ready to start calling I wrap the blanket around me, covering me and my gun. I hold the blanket closed in front, and this not only cancels any movements other than my head, it gives me the opportunity to get ready under the blanket so that I only have to stick the barrel out the front and raise the gun to my shoulder. At that point if the blanket falls, no big deal, I'm ready for the shot. Most often the falling blanket is not even noticed. Plus it does get warmer under the blanket, and helps sitting longer before the cold forces me to move.