there are two (well three ways) to do this.
Two of which involve a spray paint like product called plasti dip.
You can use this just by masking off the parts that u dont want plastidipped and then spraying away. If you are worried about getting any on your paint i have seen/heard of people taking the bumper off and then taking the ring out. Cool thing about plasti dip is that it does come off if you want to redo it or if you get sick of the look. People plasti dip there rims even. I have had plasti dip on my front ring for about a year now and i am still yet to see any wear. Also it only runs for about 5 bucks a can.
The third way to do this is by getting vinyl tape but i am not sure of the dimensions and whatever. Maybe somebody else can clear that up.
Enjoy!!