Do you mean rtg? And highbackrtg? From what I know it's the qquality rtg are lighter and the hbrtg backs tend to be more darker and body more gold the higher quality is the cross back there's bbxb which is blue base cross back and another one I think lol hoped I helped!
They are labeled according to how high the color goes up their back and of course crossback means the color crosses over the top of the back. Any information on this can be found all over the internet.