Thanks for all of the replies. I use a 3nm hydrogen alpha filter to get the red nebula. This is then combined with the red channel.
Processing, all done in PixInsight:
Calibration and integration of the subs.
Noise reduction of the red green and blue channels using the techniques from Jon Rista. (TGVDenoise and Multiscale Median Transform with masks)
Linear Fit to the green channel.
Channel combination of the red green and blue images.
Gradient removal with Dynamic Background extraction. If first did this on the individual channels and it ending up being a mess with blotches all over the place. Worked perfect on the RGB image.
Photometric Color Calibration using defaults.
Conversion to Non linear using Histogram transformation. Adjust the three channels to overlap.
Generated a mask protecting everything but the galaxy.
Curves, saturation, sharpening of details in galaxy
Dark enhance script.
All these steps are at LightVortexAstronomy including an actual M31 tutorial.