Zac Posen is entering a crucial and tricky territory in any designer's career. He's no longer the new guy, but he hasn't quite gotten to the established phase yet. He's a nightlife fixture, but he's also a serious businessman with an investor partner (that would be Sean "P. Diddy" Combs, who bought part of Posen's business in April). And he's laid claim to a design aesthetic so specific he runs the risk of self-parody.

But so far, so good. The spring collection, called Trinity (and sponsored by Cartier), showed Posen capable of handling all that and then some. The look he chose to open the show spoke volumes: a simple white jacket over tailored trousers, instead of one of his famously pieced and fitted dresses, that seemed to declare, "I can do sportswear, too." He followed that with a group of clean white pieces like pencil skirts, knit dresses, more trousers, polo shirts, and a trench (done Posen-style, with lots of tiers). Then came the vivid colors and pretty dresses so beloved by the party girls—like the chain mail, argyle dress that Karolina Kurkova had swinging down the runway. Were there a few sour notes? The orange fantail coat and the patchwork-and-pastiche dresses needed to shed some of their excess. But Posen proved himself again with the palate-clearing closer—a trio of elegant black evening gowns, each ornamented with a billowing cloud of a cape that had even this jaded crowd oohing in admiration.