Detecting DSO colours depends on a range of factors: Sky conditions, nature of one's eye, quality of eyepiece employed, viewing experience.
- Sky conditions: Clouds or bad transparency, usually lead to no colour detection.
- Eye nature and experience: Older eyes detect less than younger eyes, but can make up by being used by a much more experienced observer that knows what they are looking for. Some women can see into the Ha red range, which men tend to not be good at.
- Quality of eyepiece: In my opinion, once one is an advanced amateur astronomer, quality eye pieces can make a difference.
In the Orion nebula:
- Cheap plossl: black and white colour
- Quality plossl ( Televue, Baader Ortho Classic): green minty/ blue colour
- Top tier eyepiece ( Televue Delite/ Baader Morpheus): green minty/ blue colour plus hints of pink in the Orion Nebula wings.