Taking light readings off palms makes the assumption that everyone has the same skin color as back in the TV days of Leave it to Beaver and Andy Griffiths; and even then there were those with deeper tans. Makes no difference, a midpoint reading isn't likely to give you an accurate estimate of bright snow tonality and sparkle itself, unless you have a lot of practice with that very scenario. Gray cards, if you can find a decent one, can be helpful in moderate contrast color scenes, because color film saturation is based on a midpoint. But differentiating life and sparkle versus general highlights in fresh snow or gleaming ice using b&w film can vary quite a bit from midpoint depending on circumstances. In Zone lingo, if mid gray is Zone V, those highlight gradations might be anywhere from Z 7 to Z12 or more, hardly something you want to guess about. Open sun can pose a much greater contrast range than the soft light of falling snow. And what looks OK on the web might look as flat as a soggy pancake as an enlargement in print.