Does anyone know why I have a ring like this on one lug nut per wheel? On the front one stud per wheel is painted green, and on the back one stud per wheel is painted red. Any ideas?

 

That ring is to hold the hubcaps on steelies.

 

I would guess that someone had locking lug nuts (one per wheel) on those wheels at some point. They removed the locks and replaced the locking lug nuts with lug nuts from a Honda that had wheel covers on it, as someone already stated, Those plastic rings hold the stock plastic Honda wheel covers on steel rims. Since you're running aluminum wheels on your car, you can just twist those plastic rings off the lug nuts and re-install the lugs nuts and torque them to 80 ft lbs.