The Great Katherine Heigl Hair Mystery of 2010 has been solved!
The naturally blonde Heigl told UsMagazine.com why she suddenly went brunette at Thursday's ShoWest Awards at Bally's Las Vegas, where she was honored as Female Star of the Year.
"It's for a role we haven't even begun pre-production on," Heigl, 31, told Us. "It's based on Janet Evanovich's novel One for the Money." The actress will play the role of wisecracking New Jersey detective Stephanie Plum (Author Evanovich's hit series spans 15 books so far.)
"She is a very specific kind of girl, so I just wanted to show the legion of fans that I will be your vision of Stephanie Plum. It's important. I hate when my favorite books are made into films and they are just not what you expect."
Heigl -- who had a wardrobe malfunction that night when her dress strap broke -- admitted the new 'do took some getting used to. "I was pretty shocked at first...I was like, 'wow, it's dark, that's not just brown, that's black.' It took me a good day and a half to totally embrace it."
Her husband, Josh Kelley, "just freaked out immediately," she added. "That's good at least that the boys like it."
Life as a non-blonde is great, she gushed. "I love it. It's fun. I feel a bit different even though I don't act any different. I say all the same stupid things -- I just look different."
Heigl wouldn't confirm recent reports that she's left her show Grey's Anatomy after a rocky six years.
The actress had taken some time off from the series to bond with Naleigh, her adopted 16-month-old daughter.