Right. So according to the last few Green Lanterns, there is an emotional spectrum and each emotion can be manifested into a sort of energy that can be channeled by alien super-science into controllable devices.
Right now, the spectrum has been mapped out thusly, with a faction manipulating said energy for their own ends.
Yellow = Fear = Qwardians
Green = Willpower = Guardians
Violet = Love = Zamarons
And then in the latest issue, the Zamaron leaders noted that the further one goes from the middle of the spectrum, the easier it is for a "host" to be consumed by their power. Hence the reason why all of their Star Sapphires went a bit loopy.
But the Zamarons also made reference to a prophecy and how they must learn to master the whole spectrum. This begs the question... what else is on the spectrum?
Well, I think Red is easy enough to puzzle out. Anger or Hate - whatever you want to call it. Something set directly apart from Love.
Blue, to continue the trend, is probably Depression. Which is a rather poor thing to defend the universe with. What do you do? Command your blue ring to play Morrisey songs until the bad guys surrender?
No clue what Orange and Indigo will do. But it does make me wonder about what Corps we may see at the end of this. ;)