Again, I will suggest
Taye Diggs for Curtis
& Jamie Foxx for James...
and casting Beyonce is not a mistake. The show is based on the Supremes, but is not an Actual true story (if it were, they would have used real names.) Beyonce is perfect for Deena because she is light skinned and has blonde hair. She appeals to the white audiences today just as she would have in the sixties. Their smartest move would be to get her, because non-theatre-goers would attend this film, and make it the next best thing to Chicago. Wether or not people don't see her as Deena is not the issue when transporting a musical to a movie. Producers want money. It's really not a bad casting choice either. And by the way, Diana Ross is light skinned compared to Mary Wells. Diana was the lightest of the three.
Keep in mind, people, that Broadway actors are not huge box-office draws, unless they have created a name for themselves in movies (i.e. Nathan Lane or Rent, which has Taye, Jesse, and Rosario Dawson as their big names). A Lot of people mentioned so far in this thread are unknowns to the mainstream audience. And unless they get bigger stars for the other parts, those few don't have a chance. Honestly, who will see Dreamgirls with unknowns? (and I'm not talking about the loyal Broadway folk on this website)
"Do you know what pledge time is, Andrew"? said the PBS Executive.
"Yes", Lloyd Webber replied. "My 50th birthday special must be one program that gets done a lot."
"No", mused the man from PBS heedlessy. "Not so much. Our Stephen Sondheim Carnegie Hall concert. That's a big one."
Spoons, forks and knives seemed suddenly to suspend their motion in horror, all around the table.