Texun, Which R9 do you have?
I've looked at my R9 a whole lot since I got it a few months ago. Mine is the Stealth as I like all black guns. Before I got it I had heard of the Diamond Black finish, though I really didn't know what that was. I figured it was some kind of hard blue finish.
Yesterday I happened to look at my R9 in the sunlight. For a moment, I wasn't sure it was the same gun. The entire finish burst with every color of the rainbow. It was as if the surface was covered with microscopic diamonds. Hence the name.
I would not consider refinishing an R9, unless there was a problem with the factory finish (IMO). Although, I have considered refinishing my Springfield XD in digital cammo.