Is there a way you could apply this across the whole map, including the immediate vacinity of the player just for night time, so that night time looks more realistic? At the moment, native it really isn't dark enough. They've just dimmed the lights slightly and changed he sky box.
Normally, you would use black fog, and turn skybox fogging off.
Good news - since .9xx you can vary fog distance and color via operations in module system, at last you can deal with that annoying default fog.
Bad news - it is, as usually, broken.
If you set the fog color to zero, it appears blue! ways too bright for the task, it is brighter than the night skybox, so unfortunately we can't use it.