Can confirm, that adjusting the gamma... will leave the mod settings for nighttime, as they need to be... while making things a bit less... like feeling of being in a closed in well or bank vault.
I bumped My settings up to a read of "53" on the "GammaCorrection" setting, just enough to be able to see but still retain a sense of it being night.
Sample of My 'GFXSettings.cfg' file, located in the save folder:
[Current]
DepthBufferEffects=1
Filters=1
Glare=1
UnderwaterDispMap=1
LightShafts=1
3DShipWakes=1
DetailedWaveRipples=1
UnitNormalMaps=1
ShipCausticsEffects=1
Ship3DDamage=1
CharacterDetail=1
ParticlesDetail=8
TerrainObjectsDensity=6
TerrainObjectsLODSize=8
GammaCorrection=53
VolumetricFog=0
Hope this info helps...
M. M.