"The Sex Lives of College Girls"'s Costume Designer Breaks Down Each Character's Look

As Leighton comes out of her shell, her style reflects that growth. She starts sporting pieces with a little more edge and color, though her wardrobe still stays true to her sophisticated, New York City private-school-girl roots, with silky, expensive fabrics and designer pieces. "She's definitely a little less buttoned up this season," Mellow says.

Ranging from Gucci and Veronica Beard to Lacoste and Zara, Leighton's outfits mix both high-end and affordable items. She may not wear turtlenecks to frat parties anymore, but she loves a structured blazer and striped cardigan.