This is hardly rocket science but I am CALLING IT NOW so ALL YOU BITCHES gotta pay respekz when I am proven right:
White is the topmost color on the visible light spectrum (I dunno if "topmost" is the right word but you get my drift): if you put a rainbow through a prism it's come out white, yadda yadda. So the climax of Blackest Night is going to feature Hal Jordan getting his hands on one of every extant power ring (cue the homage to this) and then becoming the all-powerful "White Lantern" with the power to destroy the Black Lanterns just by looking at them funny. And then he'll recite this oath:
In whitest dawn, in purest pale,
No color shall escape my bleach,
Let those who mess with honkies quail,
Beware my stain-fighting power, Clorox Lantern's gonna getcha*.
* This didn't rhyme well.