This is my whack at a three part Green Lantern ring. I made it for a friend who is size 11.5 (US/Canada units), put another way, the inner diameter is 20.6mm.
If you want it in a different size, I am not sure I am ready to parametrize this, but shoot me a message and I can share the 123D file and walk you through my math.
Printer: Flashforge Creator Pro
Rafts: Doesn't Matter
Supports: Yes
Notes:
I am using glow in the dark PLA for the insides and green T-Glase for the smoky green logo. You can use black or metallic PLA for the blackish section.