What the heck is going on???
There are two categories of reasons why:
The primary reason is human eye physiology. Our eyes while exceptional at seeing detail and colour under brilliant light, in the dim light that we do our astro, our human eyes are very poor. The resulting image is a "default" one of black and white. In dim illumination, our colour sensitive cones are not fired up enough to trigger a response. The rods in our eyes are able to be fired, but the image they produce is essentially a black and white one.
However, colour can be seen in some deep sky objects, and namely nebulae, but the variety of colours and their brilliance has a lot of "depends" reasons. And these reasons are why some people can see colours in these DSOs, yet other people see no colours what so ever.
The secondary reason for colour perception:
* Gender: 1/3 of all males have some degree of colour blindness, from oh-so-slight through to no colour perception at all (very rare). Yet colour blindness is rare in females.
* Age: Colour perception at low levels of illumination can change with age. I can atest to this! When I got my 17.5" scope about 8 years ago, the very first object I looked at was M42, the Orion nebula, I was able to see pinks, blues and greens in it! Yet today, same scope, and even better eyepieces, yet I have lost those lovely pinks, and the blues and greens are much less vibrant. Yet there are some lucky individuals whose colour perception doesn't change. <sigh>
* Health: Whole of body health can affect eye health and vision. Diabetes, smoking, excessive alcohol consumption, drugs (perscribed or illicit), and a myriad of other health complications can all work against not only colour perception, but also visual acuity.
* Genetics: One card we have no control over, and have mum and dad to thank for. There are some genetically inherited traits that mean some individuals have exceptional low light colour pereption, yet others struggle to see much at all little lone colour.
And of course, the whole lot of the above varies between individuals!
But all is not lost!
So, if at first you don't see colour, be patient. Looking through a telescope is a very different experience that our "daylight" accustomed eyes are used to. It takes a little time to re-train your eyes to see under these unique conditions. One part of this re-training process is to use "averted vision" in order to maximize detail perception. I'll elaborate a little more on averted vision in a following post here.
DON'T RUSH! Take your time, and be calm at the eyepiece, and you will allow your eyes to adapt. Rush, and you are only cheating yourself.
Do these things, and if you are one of the fortunate individuals with good low light colour perception, and you will be rewarded. There are not very many objects that do show us colour through the telescope, so if you cannot see colour, don't be disappointed. Heck, I've lost my ability to see those vivid colours in M42... 😭