I was almost tempted to make the dominate colour green, but settled for this nice blue instead.
Recently I did GUM-15 in Ha as a mono and there's a lot of data there for it. So I thought I'd add some other NB channels. OIII turned up nothing in a test, while there was a bit of SII. The problem is, that the SII is just so faint compared to the Ha and does not really distinguish itself from the Ha, that the end result isn't much more than a Ha image anyway.
So, if I did it again (or extend this), I'd probably just do RGB, maybe add the Ha and move on.
Acquisition details, etc and a slightly wider field version on astrobin:
https://astrob.in/ik7lly/0/