Green Lantern, Vol. 4 #37B

The Blue Lanterns expand on their plan to recruit Hal Jordan as their leader. He's willing to help them get Sinestro back from the Red Lanterns, but only on the condition that Sinestro comes back to Oa for Green Lantern justice. Hal's rage is further fueled when he is captured by the Red Lanterns along with Sinestro, only to watch helpless as the Sinestro Corps free their namesake, allowing him to attack Laira. It is in this moment that Hal finally forsakes the Green in favor of another color.