OK, I have also been asking about this on this board and other boards, even searching through the net if colors other than green are visible. Don (posts as Starman) told me it is possible and that he saw pinkish hues in the "loop" area in M42 with a 90 mm scope...
Well my search is over. Last week I set up my 6" scope in the backyard and took a nice, good, long view at M42. Color WAS visible
It was mostly noted at 45X with an Orion 26mm Highlight Plossl. I was seeing the regular greenish color in the Trapezium region, but upon closer inspection I started to see pinkish hues in the fainter "loop" area in the nebula as Don pointed out to me.
It had always been there, right in my face and I never noticed it. The pink hues were seen with out any filtering and with direct vision. They are VERY subtle but if you look long enough and from a dark site you will see it.
For reference, my NELM is about 5.5 and probably a little deeper at zenith. If your NELM is not that deep I would recommend larger aperture if possible and higher mag. for extra contrast.
-------------------- Diego
Celestron 80 mm f11.4
Oberwerk 20x90
6" f7.8 Reflector