I reprocessed my M20 to include M21 (which meant discarding a bunch of rotated subs) with a view to keep the colour relationships between the Ha, [OIII] and [SII]. I still inverted the image, stripped the green (flip side of purple) and re-invreted the image to get something that resembled natural star colour. I usually strip the green after stretching the image but in this case opted to keep in to better represent the Ha. When tweaking colours I used starless Ha, [OIII] and [SII] masks rather than colour masks so that I would keep some kind of integrity to the SHO colour mix, while keep the stars mostly untouched. An odd image for me but felt the result was interesting enough.
Astrobin:
https://www.astrobin.com/full/dr0bnt/0/