It's called reputation. If you hover over the orb it will say that you have 0 reputation (that's why you have a grey orb). People give you reputation (generally) when you help them out or submit a good resource.
You can give other people reputation by clicking on the little box next to their orb(s).
You get green, blue, red, silver, and some other colors depending on how much reputation you have.
You get a yellow orb for every 10 reputation up to like 50 or something then you get a green orb. You get a blue orb at 150. And I THINK you get a silver orb at like 650 or something like that.
Red orbs are if you have negative reputation. Negative reputation is given when you've broken any of the Hive's rules or acted in some other manner that caused a moderator to think you deserved it.
Welcome to the Hive ^-^