check your gama settings for COH they might be to high. i honestly dont have that problem thats why i really dont want to mess with the lighting. there should be no reason why i can view it fine and other people heve a problem. regarding the grass, actually i dont think i used any grass, they are twigs.
you want us to put our graphics on low just to play this map? there is just one simple slide in atmosphere settings that change the amount of bloom.
edit: also look at other winter maps, those dont really have problems brightness.