Jessica Alba donned a new do for her upcoming role in the sequel to “Sin City”. The 31-year-old took to Twitter to show off the gradual transformation for her fans and followers to see. “Bye bye brown hair - r u on viddy yet? I\'m documenting my brown to Sin City blonde,” tweeted Jessica from her official Twitter account. This is the first time the actress has changed her hair colour since 2009. Alba will reprise the role of blond stripper Nancy Callahan for the sequel, which will be released in 2013.