For me, the important thing is to process Luminance and colour separately. Then I can focus on getting the detail I want in the Lum and separately worry about getting the colours right.
This is precisely my problem Rick. I've got a great looking luminance. It's the color image that I can't get right. I've got a great looking straight RGB image, but I want to enhance the red with Ha and green/blue with OIII. But no matter what I try adding the narrowband in makes the color look like cotton candy.
So, how do you combine Ha with R, and OIII with green/blue? You say "pixelmath" and "colormask"...I need the details. 
Hi Joel,
Does that mean you've already got the detail you want from the NB data incorporated into your Luminance? The whispy stuff you mentioned in your original post? Assuming you have and that you're just trying to enhance the colour one simple technique is to use PixelMath to blend NB and RGB colours.
First it is helpful to use LinearFit to make sure all the data is roughly compatible (I'm assuming you're starting with linear data). Pick one of the masters and LinearFit the others to match it. Then play around with some different mixes in PixelMath, e.g. Red=0.75*R+0.25*Ha, Green=0.7*G+0.3*OIII, Blue=0.5*B+0.4*OIII+0.1*Ha. Try a few and see if you can find something you like. You can use BackgroundNeutralization if needed (it's even worth trying ColorCalibration to see if you like the result.) Don't aim to get a perfect result - just something which is heading towards what you want.
Now do a linear noise reduction, if needed, and stretch. After that you can use masks and curves to adjust the colours and saturation to taste. Maybe you want to make the cyans more blue. You can do that with a simple Hue curve or you could make a cyan ColorMask and use curves to reduce the green, add more blue, increase lightness, boost saturation, etc. With a few rounds of adjustment you can make some substantial changes for better (or worse!)
Once you're happy with the colour then combine it with the luminance. I usually extract the CIE L* from the colour (after ensuring it has a 1:1:1 RGBWS) and LinearFit the luminance to match it before using LRGBCombination. This step will stop the colours getting washed out if the Lum is too strong. You can also play a little with the Lightness and Saturation sliders.
As an alternative to the above, a really simple way to add some NB colour to RGB data is to apply the NB as a mask and then increase the appropriate colour with a curve, e.g. apply the Ha as a mask to your RGB image and boost the R curve a little and maybe even a tiny boost in B for the H beta.
Hope that helps. I don't have a single magic bullet answer.
Cheers,
Rick.
