10. Alyson Hannigan
Natural hair color: Brown
Why she went red: It might have been for Buffy the Vampire Slayer, the show that set her on the path to stardom. Regardless, she was coy about it in an interview with the NY Post around the release of Date Movie (2006).
The Post asked, "They say that redheads are feisty. Are you feisty?" To which she responded, "I think the better question is, am I actually a redhead?"