i have no idea if there is a difference but i will tell you this.

on my mtb's i have had a silver 20t and a silver 22t; BOMBPROOF....

on my commuter i got a brown 17t, it started clunking almost right away and almost froze up after about a month till i bathed it in oil (if you hear a loud clunking time for some oil!). it still works but not nearly as well as the others.

they are all 3/32nds.... my dude at the bikeshop says it makes no difference but i am looking for a silver one next! (or just a white industries which are supposedly REALLY nice)