Have you tried to boost the exposure a little with maybe a little white balance tweak? Snow can be a pain to photograph in because it tricks the cameras metering. The white snow comes out grey as the metering is trying to meter the subject at 18% grey. It can be solved by adding around a stop of exposure compensation when taking the photo, and sometimes rescued in post processing by boosting the exposure. I always find photographing in a snow difficult, trying to over expose without blowing the highlights is something I find difficult, especially as we get very little time to practice in the snow in most parts of the UK.