I recently made a test-level that shows the use of background-and fogcolor fadings to achieve a decent day-to-night change. It also includes dynamic sun/moon and a lensflare effect and...a nice multitexture-terrain-shader.
The here shown method is suited for large outdoor levels that need a close clipping for higher fps count.

Of course there are many things to improove and I would be happy to hear from you how! As you know, I'm only able to do some kind of pseudo-scripting...ready for you to rework and post here

Credits go to Thorsten Kunze (terrainshader), Alexander Esslinger (lighting in terrainshader), Psionic (dwarf-model) and David Lancaster (modified template6 lensflare-script and flare pictures).

Note: Needs at least version 6.4... because of chunked terrain.

DOWNLOAD HERE (8 mb!)