If the skin was very thin and weakened in some way from the surgery, I suppose you could have gotten frostbite.........super unusual. Blanched white tissue that was normal in appearance before the ice and normal upon "thawing" suggests a frostbite type of event but I have never seen that before. The circulation to the skin must have been fairly poor before the ice went on to account for it.
Long story short, silvadene sounds like a good call. Hopefully won't make an open wound. Stay tight with your doc as you heal.