when you start, you probably have an idea if you want a very colorful eye candy image or if you want just a slight pastel touch. Usually I am not so much on the colorful side until I have finished the image and compare it to other versions on astrobin. That is when I go back to an early stage and try add more color. That is why this time the original is very color full. I'm posting it here not to say it must be so saturated but to discuss the colors you find in a galaxy in general. So here is my image
Galaxies evolve over time. Young stars get born in the spiral arms, the older ones gather in the center. Stars that burn blue don't live long. Stars that burn yellow or red save fuel and live much longer. That is why many galaxies are golden in the center. If there are blue stars they are in the spiral arms. That is why the spiral arms are blue. Galaxies are dirty. There is dust that fades the light to brown. That is what we see in the milky way and here as well. So basically you should end up with a golden center, blue arms and brown dust. There are Ha clouds glowing in red in the radiation of the young blue stars. This is missing in my data because it is not modded. I'd like to shoot Ha but the clouds don't let me. Anyway, golden, blue, pink, brown. What is missing? There is absolutely no green in space other than O-III which is teal but not green. Any green in an image is noise in the green channel and can be removed completely.
All the stars in the image are foreground stars in our own galaxy. They have all sorts of color that a Planck radiator can have, like a light bulb from yellow to white and blue. Again, no green.
So during procession you want to balance color in a way that all the colors are there and all the green is removed. If you finally make a neon image like mine or a more gentle touch of color is your decision but one would expect to see some sort of color variation as described above. Problem is, stretching removes color. So you either have to add saturation or you have to stretch in L*a*b* and steepen the a* and b* component. Bracken explains it in his book. In PI there is Mark Shelly's (CN: sharkmelly) arcsinh stretch that preservers color while stretching. There is some sort of stand alone version of it, I don't know the details. You will find it. No matter which tool you use, the task is to preserve the color and to keep the noise out. Not an easy task.