You're not wrong Myxale, this mod died years ago!!
As Myxale explained it Steve that is a SHIII "bug", though not really, at the time of release it was a huge step ahead for the SH series but believe me, we all tried to fix this, similar problem underwater!
Now if you could take the graphics of SHV and put in SHIII it would be almost perfect!!
Though for some reason I'm not going down that road!!
If you can find some earlier versions of the mod it included various versions of the ENV\Skycolors for differing levels of night brightness.