Britney Spears, Jessica Simpson, Paris Hilton, all the Spice Girls, etc, could go on forever.
Even all the "blonde" guy celebrities are naturally brunette (though guy are commonly called brunet). Jesse McCartney, Aaron Carter, those two kids from The Suite Life of Zack and Cody, etc.
However, note that many kids have blonde hair that darkens with age. The Olsen twins
naturally had blonde hair at one point.