SGP does not currently have a "Night Vision Mode" and we almost certainly won't be adding one in the future. Just for the simple reason that it is not system wide and only helps when you're in SGP. If you flip over to PHD, open some other application and then poof...bright white light!
There are better solutions like red acrylic (exceptionally good but somewhat pricey, but this is what I use and highly recommend)
http://www.scopestuff.com/ss_r8xx.htm
And rubylity on film (cheaper but not as optically clear)
http://www.scopestuff.com/ss_redm1.htm
Thanks,
Jared