the reason some are green, and some are blue, is a few different reasons..
first.. all flagged PvP characters, will have a green name above them. If your on a PvE server, and not flagged, you will be a blueish color.
also, if your in a group, all group members will have a lighter blue name above their head.
anyone that wants to, roll a new character on gurubashi horde, add carbon to your friends list, and hit me up when im on, and we can get you to 70 quick.