First up, coloring is indeed a preference thing to a degree. It's a complex story, but the crux of it is that color perception is subjective and also that there is no one accepted white point in outer space.celeron787 wrote:May I know when to leave the color module as default selection and when to use a star mask sample? Both yield quite different colors. Is it a preference thing?
What is not in question, however, is that some manipulations are - from a documentary/photographic point of view - big no-no's. These include using curves on individual channels or brightness-based hue manipulations.
Back to establishing a white point; have a look here for a good few techniques. Indeed sampling a bunch of stars is one of them. However, sampling just a few bright stars is a bad idea if you optical train suffers from chromatic aberration, skewing the colors in the stars, as is the case here; the purple has no business being there.
Instead I just sampled the whole image, knowing that the aggregate should be good "millky" white reference. You can use the same technique for most other nearby spiral galaxies; the aggregate star light in them should be roughly white.
Hope this helps!