Jessica Simpson take note: In one week, both Britney Spears and Paris Hilton have taken a walk on the dark side, ditching their blonde tresses for new black dos. And what does a girl do when she goes edgy? In New York City, Spears went on a shopping spree with 9-month-old son Sean Preston in her arms, picking up several pairs of sunglasses. Hilton, meanwhile, only made a temporary tress-formation: She donned a long, black wig at London’s Wireless Festival, where she chatted up Gnarls Barkley frontman Cee-Lo. All we need is one more flaxen-haired celeb to go brunette and it’s a trend.