The cause is a perceptual issue. Your camera sensor has a linear response to colour at different levels of brightness, but your eye has a non-linear response. We perceive far less colour in darker parts of a scene than we do in the bright parts (rods vs cones). So when you see your final image on screen, the dark (coloured) areas of the subject can look over-saturated, often horribly so.
The solution is simple - desaturate shadow tones (only). In Photoshop and Affinity this involves creating an HSL adjustment layer with saturation turned way down. Crucially, a mask is applied to the adjustment layer so only shadow tones are affected. In Affinity, the mask is created using Select/Tonal Ranges/Shadows then create the HSL layer. It's a little more complex in Photoshop - the channels tab is probably the best route for selecting only shadow tones (look up "luminosity masking" for details). In fact, luminosity masking is probably the best method if you want fine control over which tones are affected. But the "select shadows" method in Affinity works very well in most cases.
Here's an example using the Sicus sp(?) I posted yesterday. First, the result from stacking and doing overall exposure adjustments...

And now the "improved" version with shadows quite heavily desaturated...

And finally, the mask that was applied to the HSL adjustment layer (in Affinity Photo). White parts get full adjustment, black parts get none, grey parts are adjusted proportionately. Note: this one is fairly bitonal, so not much grey in evidence. Luminosity masking tends to produce a much smoother transition between tones - and yields a "grayer" mask as a result.

So that's it, my tip for the year, or two
