Re: Orion nebula
Though it can only be a partial disappointment, that is a composite photo taken by Nasa using filters of varying wavelengths, with each color representing a different gas. Whoever worked on the project could assign whatever color he or she wanted for each of the wavelength ranges.
The nebula is nonetheless spectacular and most people who report any color using backyard telescopes with UHC filters to filter out light pollution and designed for nebula viewing describe seeing it as grayish green. I've seen it through a filter that was projected as looking pink with a little green.
Each of several gasses, the most predominant of which is hydrogen, glows due to the intense UV radiation that is emitted by four hot, young stars called the Trapezium Cluster.
Of interest, Betelgeuse, Orion's upper-left shoulder is undergoing unprecedented dimming, which was not expected.