Don’t Want Gray Snow?
Left on automatic with no adjustments, cameras render white scenes like snow as gray. The reason for this is that the camera is designed to perceive every scene as medium tone in the absence of any other information and sets the exposure accordingly. Therefore, it underexposes very light scenes making them darker than reality, and overexposes very dark scenes making them lighter. To keep your snow white and use the automatic setting for exposure—P—on most cameras, add one and a half to two stops of exposure using the exposure compensation controls in your menu. If you are shooting in the manual mode, overexpose by that amount in your shutter speed/aperture settings. Taking these steps should rid you of gray snow.