StarTools

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?

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.
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!