I am wondering whether they will feature a black or a white Green Lantern.
As Taz mentioned above it will be John Stewart, the 4th Earthman to become a Green Lantern, playing the part.
Just a little GL history here for anyone not familiar with the character...
The first GL in comics was Alan Scott. He fought during the golden age of comics for the Justice Society of America during WWII but was never an actual member of the GL Corps and his ring was mystical in nature instead of alien. His ring had different properties than the other GLs had including a weakness to wood.
Personally, I think they should use the original mainstream silver age GL, Hal Jordan and introduce the others later.
The GL I grew up watching on Superfriends, Hal was the best of the best. Even after going mad after being possesed by Parallax, the evil manafestation of fear incarnate known as the yellow impurity, Hal redeemed himself and was killed to become The Spectre. He later returned to life as a Green Lantern again although many Corps members remember the lives he took while posessed by evil.
Guy Gardner was selected by the Guardians to replace Hal Jordan. A different kind of hero and generally not a liked guy by many of his team mates because of his straight forwardness and sexist attitude but Guy always did the right thing in the end.
Then came John Stewart to be Gardner's replacement. Just as heroic as Jordan he's filled in on Earth many times when the designated Lantern had left for the stars and is currently rotating shifts in the JLA with Hal Jordan.
The last Earthman to become a GL was Kyle Rayner. After the whole Hal Jordan/Parallax situation destroyed the GL Corps several years ago, Rayner was selected to wield the last GL power ring in the universe.
Since the rebirth of the Corps and thousands of new GL recruits from all over the universe Rayner had become possesed by the manifestation of willpower, Ion, which is Parallax's counterpart. With raw power at his will he needed no ring.
During the current Sinestro War between the Green Lantern Corps and the Sinestro Corps, Ion was imprisoned while Parallax possessed Kyle.
He has since taken a ring and is once again a member of the GL Corps.