The light meter in most cameras assumes that the ‘average’ of an image is what photographers call ‘neutral grey’. In most cases, this works reasonably well. However, snow and sand are both brighter than neutral grey and, if they comprise a significant portion of the image, the result will be an underexposed image. This is why snow and sand take on a dull grey colour in many photos. While you may be able to adjust this later, in your photo-editing software, the common solution is to increase the exposure by approximately one stop. If you can’t do this manually, check your camera’s instruction manual. Some cameras have a ‘beach’ mode designed to address this issue.