I observed m42 a couple of months ago through a 120/f5 achro + 28mmEP and it appeared grey-blue with some faint pink in the bright bits coming out from the core. I was very surprised to see any colour at all and I thought perhaps my brain was filling in what I expected to see as I've imaged m42 previously and am familiar with how it 'should' look. Also as I was mainly imaging I was only allowing myself about 10 minutes to dark adapt between observations.
I observed it a few times over about 2 hours while observing other things and tending to my imaging equipment and it looked the same each time.
M42 was probably between about 35-50 degrees and it was at Mt Wilson so not super dark.
It kind of looked like this but the pink was less pronounced and a bit less detail (and a much wider view):
http://www.astrokev.com/wp-content/u...-reproc-a1.jpg