David, having a look at your M83 you just took, expand your histogram and you will see that it's colour bands are all over the shop. The galaxy is far too red. Galaxies are too far away so see much if any nebulosity so they should be mostly white from the stars. Using the histogram is the trick. A simple Auto Tone, Auto Contrast, Auto Colour will get you close. and then do some twiddling with the Colour Adjustments.
With dedicated astronomy software more can be done but I only have Nebulosity and Photoshop with Noel Carboni's tools at the moment... Here is a 2 minute re-edit to show you what i mean. This is an excellent example of how the CLS filter messes with the colours.
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