"Green dot are allies, Blue dots are "random people" (as in, random NPC) you get to dialogue with. Dialogues don't need to be important, it's just a dialogue scene, opposed to the normal fill-in NPC responses that don't trigger any dialogue."
Sounds about right.
http://www.gamefaqs.com/boards/975399-/59165028 --- Stand and deliver, that my hamster might have a better look at you.
I assumed it was Green dots were NPC's linked to some of your current quests. And Blue ones are side-mini quest/conversations you can have with those people. Maybe I'm wrong, but that's the impression I've gotten while playing the game. --- To the mattresses. PSN: Justice_98405, Xbox Live: Justice98405