The only benefit I could see of having different colored IDs is to differentiate between Steam Players and people playing on just the normal blockland launcher.
I don't see why you would need to differentiate between the two.
All you're doing is adding another level of difference for people to be prejudice about.
It's bad enough with people picking on High BL_ID's. Atleast after the next 10k milestone is reached, no one really cares much about it. If you give old players Green names, and let new Steam users have Blue names, then no matter how much time passes, people will be pointlessly and stupidly prejudice against Steam users for being "new".
If someone purchases the game through Steam or through Blockland.us, then either way, he's paid the full amount to Badspot and has earnt the game. Makes no difference where he purchased the game from, so long as he had legitimetely purchased it.