Spiney. I can see green shading in the Orion Nebula in my 10" Meade dob, depending on conditions. I have also picked up a little pink on occasions. You should have no probs with seeing colour in M42 with a 12" dob providing you have reasonable eyesight.
The reason we do not see all the colours like the photo's is because our brain/retina, processes the photons immediately. Unlike a film or CCD chip which accumulates them...
That is why the No.1 rule is "Aperture Wins".
More photons = more resolution/definition & colour.
HTH.
L.