Thanks for all the suggestions guys : ) I think I've got it about as dark as it's going to go now! It's certainly dark enough that I've come close to stuffing it into the dirt a few times : p
To do this I extracted the ENVIRONMENTSYSTEM.INI from the FlightData.cat, and made changes to the following sections:
[Night]
SunHeight=-0.170
SunBrightness=0.00
SunLightLevel=0.00
SunRadiance=0.0
TwilightLensFlare=0.0
SunColor=0.0000,0.000,0.000
AmbientColor=0.04,0.03,0.05
SkyColor=0.01,0.01,0.01
HorizonColor=0.0,0.0,0.0
FogColor=0.0,0.0,0.0
SunSpecularColor=0.0000,0.000,0.000
[Moon]
MoonMaterial=MoonMaterial
MoonSize=13.0
MoonMaxLightLevel=0.0
MoonLightColor=0.980,0.933,0.478
OvercastAmbientModifier=1.0
OvercastDirectModifier=0.8
MoonTextureFormat=Moon%03d.tga
NumMoonPhase=29
NewMoonDate=09/22/1968
I believe it was zeroing out the MoonMaxLightLevel value that really made things get dark : ) It is still possible to see the ground with these settings, but it's rather murky on the other side of the canopy now...