From what I can gather(but may be totally wrong about this), the green dots show your rep level. We all seem to have varying numbers and darknesses of green dots because we all are "nice" and don't have bad reps. I think if a person starts to get bad rep points their dots will turn red letting other people know that this person may be a troll, spammer, or just not a nice person. That's my take on the whole thing, sound right?