Jessica Alba is finally beginning production on Sin City: A Dame to Kill For, and the 31-year-old actress tweeted some photos over the weekend of her new hair ... and her killer prep work for the sequel!

"Stage 2 of #SinCity2 Nancy hair ... She got roots that Nancy," she wrote. "What a way to start the day - training for a movie is sorta fun."

The follow-up to Frank Miller and Robert Rodriguez's 2005 hit follows Dwight (previously played by Clive Owen) as he "plans to have his vengeance against the woman who betrayed him, Ava Lord, while Nancy is trying to cope with Hartigan's death," according to IMDb. Can't wait to see where this goes!