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Hi, Erik,
I like your image a lot. This galaxy has famously low surface brightness making it far harder than you'd expect, especially in light pollution, so top job.
You asked about the colour. I'm the world's worst to comment, because I'm colourblind, but that means I've spent more time "doing it by the book" and thinking about the astrophysics, rather than subjectively. Doesn't mean I get it right, but here's a possible recipe which is heading in the right direction:
- Measure the average colour of bits of starless background. It ought to be close to neutral and very dark but nowhere black. Set the zero point for each channel accordingly. Do this first. If you can't measure the actual RGB values of the averaged background, looking at the histogram can help a lot. Set the black point for each channel so that the bottom of the histogram is almost, but not quite, zero.
- Measure the average colour of the entire galaxy. Magellanic galaxies can be very blue, and distant, dust-obscured galaxies can be very red, but most face-on spirals should on-average be approximately neutral. The brightest, most conspicuous clusters of stars in the spiral arms will be OB stars and therefore blue, and the stars in the core will mostly be very old stars and therefore salmon pink. But don't try to make them that way, just adjust the white point on each colour channel until the average colour of the galaxy is neutral. Then, hey, presto, the blue spiral arms and the salmon pink core will spring out automatically. You can then (according to taste) carefully increase the saturation in order to bring out subtle differences which have been hidden by a strong nonlinear stretch.
I had a go at doing this with your shot, and it works. The core ends up more salmon pink, the spiral arms more blue, and the field stars come out a pleasing mixture of subtle colours.
One trap to watch using the method I've described is that some galaxies have a strong mixture of near-magenta in the spiral arms, and warmer orange in the core, and the above approach done blindly will put too much green in the green channel. So just make sure you don't have any turquoise stars.
Another trap with increasing the saturation to show subtle true colours in the galaxy is it can end up creating background colour noise. There are ways around that, using a blurry mask to select just the bright regions for restoring the saturation, leaving the dim regions unchanged, and pro rata in between. That's not necessary in the case of your image.
Others can advise you far better than I can, but that might be a starting point.
Cheers,
Mike
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