So I created new versions of the night sky images to better fit with the existing day time skies. Ideally I would also edit a few frames of the day time skies to make the transition from day to night more seamless, but I don't think modding SKY images is currently supported?
Below is a comparison of the original night sky to my new version:
Spoiler!
I've attached a zip file with the .pngs for the new night skies. To get them in your game, just copy them to your "StreamingAssets\Textures" folder. Note that unlike other IMG files, these *do not* need to go into the Img subfolder.
Also, I thought I would note that even though these are low-res image replacements, they look fine without disabling modded texture compression in settings.ini - I guess the darkness of these images makes the compression artefacts difficult to notice.