I have tried this many times, but I can assure you, that on low and mid graphics there is no such things like stars on sky.
There is no night time sky texture, as far as I can tell. This would be an easy fix to mod.
Alright, I take it back. I was under the impression that the OP was claiming the sky looks exactly the same as night as it does during the day, which I don't think it does. It's true, though, that there's no special skybox with stars, only that it's a darker blue - I never really thought about it until now. :|