Originally Posted by
GrumpyDiver
Matt - if the clock on your camera is set correctly, you either had a very heavily overcast day or (more likely) your camera's light meter was fooled by the snow. While I'm oversimplifying a bit here, the assumption built into a camera's metering system is based on an average scene, which could translate into the same overall density as "neutral gray".
Snow is, well "snow white", not gray or some other tone, as per your first two images. This means you have to override your camera's natural tendency to underexpose snow, by using exposure compensation. I usually start at +1 and check my histogram and go from there; adding or subtracting exposure in 1/3 stop increments until I'm happy with it. Unfortunately, there is no "rule of thumb" you can use, as every situation is different.
The second issue with snow (being white) is reflects other colours. On a sunny day, in open shade, snow usually has a blue tone, colour reflected by the blue sky, So in that kind of lighting one really has a "mixed lighting" situation, and colour correction can be a bit complex. The colours in your second shot are quite strange; I don't think the simple colour temperature change that Jeremy suggests is necessarily going to work. What colour were the clouds when you took the shot?