All white people carry an approximate grey card around with them. It's called your hand. If you take the light reading of your skin it will be approximately correct for snow in the same light. It is a useful trick for a lot of exposure problems. For dark skin the palm is still light so it might work, but I'm not in a position to test. Otherwise I find 2 stops bias is a bit much. I'd go for 1.5 to 1 2/3 and, yes, a mild yellow filter.

David.