I asked drlava to include red, green, blue and intensity variables for usage in expressions in the next update. If that gets added, not only will you be able to control indiviual colour levels, but also advanced colour effects such as saturation.
Would be really great!

What do you mean with "starting masterbeam messes my setup"? Each masterbeam cue has its own slider settings, they're not global. If you want global settings, stretch out your sfx over all timeline segments.
Turns out my midi sliders started controlling masterbeam sliders+effects I've put on them at the same time. I haven't played with masterbeam midi control much yet, though some key remapping should work.