THE TREND: Gray/Silver THE KEY PIECE: Leather vest with zippers, Walter, $448; searlenyc.com. WHY THIS WORKS: Tough leather looks great with a sweet dress. SHOP THE LOOK: A Necklace, Banana Republic, $70; bananarepublic.com. B Bracelets, Made Her Think, $132 each; madeherthink.com. C Dress, Margarita Saplala, $255; 212-352-1640. D Sandals, Fergie, $100; shoes.com. E Bag, Helen Kaminski, $775; ebags.com.