On coming up with a more meaningful 3 color pallet:
In a previous post on the clown nebula, I discussed the relative contributions of Ha and NII emissions to the image, but used a relatively traditional pallet for the image, assigning NII to red and OIII to teal (the “true colors”). I subsequently came up with a more meaningful 3 color pallet in order to illustrate the differential Ha and NII emissions (both red): I assigned NII to red, Ha to green, and OIII to blue, then balanced the NII and OIII on the "smile", making it orange. The net effect was a variation in the color of the NII globules depending on the ratio of NII to Ha with red having more NII, and green more Ha relative to the "smile". Also note the blue (OIII) section just above the central star, and red NII outer rim of the "nose" upper left.
In more quantitative terms, for the linear images I measured about 200 adu NII in the smile and 700 adu with the 5 nm Ha (Ha+NII), which implies 500 adu Ha, so more Ha signal than NII. Over all, I find the NII provides more contrast and, arguably, a more interesting image.
Imaging details in previous post.