Gwen Stefani kept her Cannes Film Festival fashion coming this evening at the premiere of Sean Penn's This Must Be the Place, choosing a black-and-white gown with strategic cutouts. The singer went solo for the red-carpet debut after her husband, Gavin Rossdale, caught a flight out of nearby Nice this morning. Gavin and Gwen were together last night, though, for the amfAR Cinema Against AIDS fundraiser along with Kanye West, Bar Refaeli, and other stars. Sean was also by himself for today's unveiling of the film, without girlfriend Scarlett Johansson. Gwen's cycled through a collection of gorgeous gowns and dramatic outfits during her time on the French Riviera, but her trip hasn't been a completely formal affair — Gwen wore a bikini while enjoying the sun on a yacht with Gavin, Zuma, and Kingston this week.