[Vpmedia]

try to create a file c:\Program Files\Ubisoft\IL-2 Sturmovik 1946\MODS\MAPMODS\maps\_Tex\CloudShadows.mat

its contents should be

[ClassInfo]
ClassName TMaterial
[LightParams]
Diffuse 0.75

there you can adjust the Diffuse 0.75 value probably between 0.1 and 1.0

try 0.2 for example and see what it does