She's best known for playing the mysterious dark beauty "Thirteen" in the TV show "House," but Olivia Wilde had her big break playing a blonde on another hit TV show, "The O.C." back in 2004. Do you remember Alex, the bad-girl who romanced both Seth and Marissa? George Pimentel/WireImage.com - March 7, 2010
Do Blondes Really Have More Fun?
See which stars have traded in their naturally blond locks for darker 'dos.