It's that time of the year for some fun in the snow! It may be on the slopes, in the back yard, or the traditional Hallmark snow-ball fight. Now your camera wants to make everything look properly exposed. It thinks the best way to do that is to pick the middle brightness and make that grey. The problem is you want the snow to be bright white, not dirty grey. The solution...use your exposure compensation to open the lens up 1-1.5 stops.
Okay, I lost a few of you--don't worry. The camera sees all the light bouncing off the snow and wants to make the photo quickly--thus the grey snow. If you see that and your camera has an exposure compensation adjustment, use that to manually add in +1 stop of time. This gives the camera a little more time, and thus light, to make the photo and the snow becomes whiter.
Also, don't be afraid to use your flash outside on those bright snow days. If your subject is near the snow's bright service their face may look perfect. If you have them in a shadow, turned away from the bright snow, or the day is cloudy, use the flash to "fill-in" the face for a printable image!