unless Shelton's participation in the film has somehow changed and I just haven't come across that bit of news yet, apparently it looks like Shelton will be doing double-duty ... (Which may mean keeping her hair blonde if that's the look Rodriguez wants for the film...)
Update:
'Sin' tempts Dimension
Rodriguez casts remaining roles; pic's opening already shot
By MICHAEL FLEMING
Robert Rodriguez has committed to direct "Sin City," an adaptation of the Frank Miller graphic noir crime novel series.
Dimension Films co-chairman Bob Weinstein has given Rodriguez the go-ahead to begin shooting next month in Austin, Texas. Rodriguez will produce with Elizabeth Avellan through his Troublemaker Studios label.
Set in Sin City, the film interconnects storylines that involve the unsavory inhabitants of the town. Rodriguez has already shot the film's opening with Josh Hartnett and Marley Shelton, and he's now casting the remaining roles as the rest of the film gets under way in March.
...
Rodriguez said the film consists of multiple storylines involving characters with questionable morals. "The morality tales and a love story revolve around this dark city, which is really the main character in the film."
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Date in print: Thurs., Feb. 26, 2004[/b]
So, not only won't Shelton be doing double-duty, but hair color speculation is definitely back in play.