Britney 's a brunette. The singer, 27, showed off the darker 'do over the weekend while shopping with boyfriend (and agent) Jason Trawick in Santa Monica, Calif. They stocked up on brooms and picture frames. ( See more photos here. ) See who had the worst hair last year Last week, a source close to the singer shot down reports that the two are engaged . Still, another source tells Usmagazine.com that Trawick, 27, has had "a calming effect over Britney." Look at all the crazy ...