I'm playing around with the weather mod again, and I'm seriously tweaking some lines in the files to see just how big an impact some of the settings have on the game.
The above three pictures are, in order, high saturation, low saturation, and no bloom. Obviously, saturation controls the color values of the game. The first picture is at 1.0 saturation, and the second is at 0.4 - there's a huge difference. However, the third picture is at normal saturation, but I disabled bloom.
As you can see, the game gets most of its light from bloom. What bloom basically does is stratch what's already there and gives a glow to it, meaning the game itself doesn't actually have to be particularly bright.
I think it's also responsible for the in-game haze, and I suddenly believe it may be possible to raise the bloom effect to make the game brighter and then mitigate the effect by shortening the bloom rays, which would bring the game back to its more familiar light levels but give it a crisper, sharper look.
Edit: Well, there's no doubt in my mind it's bloom causing this haze. This is what it looks like when the haze is put at extreme retina-annihilating levels!
Also just for fun, the sun is attacking!