Jessica Alba debuted her new haircut on Twitter and Instagram as she went blonde to reprise her role as Nancy Callahan in the sequel to "Sin City."

[Jessica Alba Haircut – Twitter @jessicaalba]

Jessica Alba tweeted some photos of her new haircut documenting the stages in transforming herself from brunette to blonde. This is in preparation for the upcoming movie “Sin City: A Dame To Kill For,” where she will reprise her role as the stripper Nancy Callahan.

Joining the 31-year-old actress in the movie are former co-stars Mickey Rourke and Michael Madsen and possibly Rosario Dawson. At the helm are Robert Rodriguez and Frank Miller and it’s set for October 4, 2013 release.

Jessica, who currently has 3.8 million Twitter followers, posted:

“What a way to start the day -training for a movie is sorta fun.”