I don't know what it's called since I'm a guy but I like it when they're like clear and shiny with white tips on both hands and toes. That look is sexy no matter if the girl is dressed classy in a dress or in a t-shirt. That one is my favorite but I do like other colors also and like it when girls change colors a lot if they're into painting their nails or getting them done.
It depends on the other colors you wear, of course, but in general, metallic silver is so soothing to watch, and usually makes a good contrast wth any bright colors you re wearing. And it's somewaht natural looking, too, which I like.