The designer, Jackson Tegu, has removed his PDF files of the rules for Silver and White. From his website (http://www.photographsoflightning.com/silver-and-white/):
The most recent version, not presently available, is called “next winter”. There have been subtle and delicate tweaks to some of the rules. If you’ve played a previous version, it would be prudent to pay close attention.
Silver and white will soon be entering its fifth round of playtesting, which will be private. Sorry about that.