Yes, I can see M42 in full colour of greens, blues and pinks.
For anyone to say no colour can be seen is only because they do not so no one else can and denies the experience of everyone else who does. And the colour that is observable is also variable for physiological reasons, greens, blues and pinks. You need to understand how the human eye functions to understand how and why colour is visible, and why some people don't
To maximise your chances of seeing blues, greens and pinks in M42 you need to match the maximum exit pupil for any given scope to the largest diameter of your pupil. This is to maximise the amount of energy reaching those cones that those specific cones that the light energy is illuminating. If there is insufficient energy density then the required response won't be triggered. This is seen in why stars can have their colour seen but nebulae far more difficult because of the much lower energy density they have. Aperture is also a factor as scopes are made to collect light - energy - and the larger the aperture the more light and the greater the energy density entering the pupil. Make the exit pupil too large or too small and the energy density reaching the illuminated cones won't be enough to trigger the required reaction. Which is why with a small exit pupil everything is seen in black and white. And the exit pupil can also vary over time for reasons that are explained below.
The eye has rods and three different sets of cones in the retina. Each of these has a different trigger threshold - so if the necessary amount of minimum energy is not reached, then there will not be a response from those cells. Rods have the lowest threshold, which is why under low illumination we see things in black and white. The green cones have the next highest threshold, which is why most people will see pale greens in nebulae through the eyepiece. Blue cones have the next highest threshold, a little higher than that for green. Red cones however, their threshold is not the same gradient up like between green and blue. Their threshold is a fair bit higher and why pinks/reds are very difficult to see under low illumination. Understand this aspect and the reason for why the appropriate exit pupil is required to trigger the appropriate colour response. AFOV is of no consequence as it is the actual illuminated area on the retina that is reacting to the stimuli of the light, not the retina in its entirety.
There are many factors that influence why some people don't see colour at low levels of illumiation.
* Age. As we age our pupils get smaller in diameter. This means that your ability to see colour in nebulae also reduces over time. So if you came to astro in older years, you may have come with a pupil diameter that won't permit enough light to get in no matter what exit pupil you use, along with other factors below.
* Gender. Colour blindness is common in males. Around 1/3 of males have some level of colour blindness, from angle's breath through to no colour perception at all (very rare). Yet colour blindness in females is rare.
* Health. Eye health has a major impact on the ability of the eye to function properly. Diseases such as diabetes is diabolical on eye health as are others. Drugs (both medical and illicit) along with alcohol and smoking are also factors that affect eye health, and hence for the eyes to function properly.
* Genetics. Something that we have no control over and may either take away ones ability to see colours or actually enhance this ability (lucky sods).
* Fatigue. This is one factor that is next to always ignored as a factor influence visual performance. Power naps are a good tool to help refresh one's eyes and one's overall performance at the eyepiece.
With people who insist that no colour can be seen through the eyepiece, when you dig a little deeper you will find that they are male, typically older and have factors that compromise their ability to see colour at low illumination or are even colour blind. Yet they feel entitled to deny the experience of everyone else.
I have always been able to see greens and blues in nebulae, of course depending on the brilliance of the nebula. I have also seen M42 in full colour of greens, blues and pinks. The first time I saw this was during first light with my 17.5" dob using a 30mm eyepiece. It blew my socks off this surprise. No "averted imagination" as this was not something that I had ever imagined possible. 10 years later as my sketching ability developed I revisited M42 to sketch it in full colour, I used the same scope/EP combination and to my great sadness I no longer could see those pinks, only the greens and blues
I thought I had lost those pinks for good.
A couple of more years and our Club has a new member, an ophthalmologist. With this I start picking his brains about how the eye works (see above) to work out practical ways in which to optimise response at the eyepiece and to work out better ways to see in the dark without compromising dark adaptation (which means I now use dim orange light to sketch with and read instead of painfully bright red which has very poor contrast and does affect dark adaptation).
Conversations with this member also encouraged me to revisit M42 with the idea that maybe it was contemporary eyepiece coatings that cheated us of this ability. So with five very experienced observing buddies we set up three scopes and armed ourselves with a bucket-load of eyepieces at our Club's dark site. The scopes we set up were my 17.5" f/4.5 dob, an 8" f/4 Newt and a 10" f/12 Mak. I was wrong about the coatings...
To our amazement five out of us six people were able to see greens, blues and pinks in ALL three scopes!
Yes, including the Mak! For me with my dob, it was needing to use a 24mm eyepiece, not a 30mm as I used 12 years prior. My pupils had reduced in size in that time so the optimal exit pupil for a full colour response had reduced. However, the colours were not as vivid now as they were all those years ago, in particular the pinks. With the f/4 Newt, I had to use a 22mm eyepiece to see all the colours. With the Mak, it required a 50mm eyepiece, and PRESTO! the greens, blues and pinks were all there!
One of my observing buddies though was not able to see any colours at all through any scope no matter what eyepiece was used. But he has significant health issues and is taking an extraordinary number of medicines. We all felt disappointed for him, but he proved to be an important control in this exercise.
I know of two people who have been able to see pinks in Eta Carina, one a 20 year old woman the other an older amateur astronomer. At outreach events I try to ask participants what colours they can see in M42 and Eta Carina. If the crowd is not too big I may also swap between eyepieces. Age is certainly an immediate factor that is seen in people's ability to see M42 in full colour (other personal factors not being discussed), and Eta Carina is certainly a difficult one to see more than pale greens and blues (as I do).
Planetary nebulae can also show colours, namely greens and blues. The Blue Planetary being the most obvious, named for its distinct hue (but apparently some people will still continue insisting that no colour can be seen through the eyepiece...). The planets, certainly show plenty of colour, but they are also extremely bright. And I have already mentioned stars showing colour.
Aperture cannot be forgotten here. I mentioned it only briefly but it is a BIG factor for its sole purpose of collecting light. f/ratio is inconsequential as it is actually exit pupil that affects energy density. But aperture grants this energy in the first place. There are astro sketchers who make use of some very large apertures, in the order of 30" and larger, that are presenting works of nebulae other than M42 in greens, blues, pinks and even yellow and orange. Make the aperture too small and of course the amount of energy is just not there to trigger the necessary response from our eyes.
So, yeah, full colour can be seen through the eyepiece, if a number of factors are satisfied and if the object is bright enough.
Alex.
...ether way, maybe something weird going on with the rose in the nebs and globs..but a perception is still part of the viewing experience of the observer, like 3D "feels" 
but the super contrasty views and vivid star colours are frikkin unreal 
...sounds like it might well be similar, or better! south of Queenstown NZ 
