Nice shot there rob.
I am with you on the Newt buring stars out, imagine the 10" 4.7.... it hurtles the photons in with a speedy sense to it!
I think the only way that you will be able to get the star colours to start playing ball with you is with 1 of 2 methods.
A. get a camera with deeper well sizes. allows longer exposures till max ADU has been achived.
B. use HDR and multiple length shots. eg, 10 5 3 1 min shots and combine them together with a HDR algorithim. but with LRGB... that could become a very very very long process
hope that gives you some ideas.!