I've not played Airsoft in the winter myself, but whenever I've asked about it I've been told pretty much just not to bother.
Anything plastic will be under extra stress below 0C, and will be almost certain to break below -5C.
Some will suggest that this depends largely on the quality of your gear, but I figure the risk isn't worth it unless you have another AEG to fall back on for other games.
GBBs nosedive in performance below +5C the farther down you go so they're not much of an answer to this question. If you have something that runs HPA you'll fare a little better.
As for camo, when I played with Airsoft's uglier sister I'd use cadpat or woodland on top and winter camo below unless there was fresh snow on the trees.
This will allow you to stand up and move around without being silhouetted against opposing colours as easily.
If you can find winter shells for the camo type you use, everything will fit well and you can add/ remove layers/ colours as needed without adding too much weight.