Thanks a lot for your suggestions. I`ll make the rainy weather setup a bit darker. Thanks to my smart weather system that`s only a matter of some sliders . @HeelX: That`s a great idea! Thanks.
Edit: Okay, I tried to find a better "rainy" setup now. Of course the level and the lighting is still not perfect. In the game it looks better because of the moving sky, the waving grass, the rain and so on