Forget Nina Garcia's obsession with the LBD: It's the little white one that's going to be your next staple closet item. Last spring's mainstay made a return appearance at runways yesterday. Siri Tollerød bounced down the runway in a ruffled number that looked like a puffy cumulus cloud at Erin Fetherston, while choppy layers flowed off a baby-doll strapless party dress at Yigal Azrouël. Then, designer-to-watch Joanne Cordero Reyes combined sleeves of sheer textured pieces with a skirt made from silky sheets in her Vicente Villarin collection. Because surely nothing signals spring more than pure white.