Hi Lex : i made a background neutralization right after the RGB combination. The area around M42 is very rich and i don't think it's really "dark" (at least, it's not when you add a strong Ha signal). A last background neutralization after processing give a greenish tone to the picture, not very beautiful.
Hi bwa : i used PixInsight color calibration and made the full processing twice, got both time the same colors. I did not play much with colors, no shift or big curves modifications, only played with saturation and the NGC1977 colors seem to be pretty accurate but i must agree that i don't know yet how to get accurate colors each time : i did not yet calibrate the RGB filters on a G2V ... and Regim do not work great on nebulaes.
Last processing, corrected the dark halos around the bright stars you might have notice in the two previous pictures (the two previous was the same processing but different color calibration : in the first one, i forgot to do background neutralization before color calibration which lead to purple colors) because of one of the HDR process i used without right protection of the stars...