Fly is correct. Rohrbaugh only had permission to produce an R-9. When they put R-9s on a few slides, it caused issues with the government. So, now all models say R-9 only.
The "s" designation only indicates the gun has sights. You have an R-9s.
Originally the guns were going to be offered with a choice of a silver frame or a gray frame. Ultimatley there were problems with the silver finish and it was dropped. A lucky few people have the silver frames. I personally like the two-tone better, but the silver ones are a rare bird and would be nice to have.
Additionally, the grips recently changed from a blue carbon fiber to a black, so the blue will eventually be harder to find.
Finally, the "gray" frame color has changed a bit over time -- there are different shades if you will.
Somebody needs to write all this down so we remember later!