how to make night sky pitch dark?

In real world the night sky is black, and quite impossible to see a clear cut line as horizon. But in FS9, the sky is dark blue in the night, I am bothered to see this line during my night flights. I have Active Sky with visibility set to 39 nm, Ground Effects Pro which I don't know has anything to do with sky, and also a free ware called soft horizon. But they all work great in the day time, so the horizon in the day light is realistic. Does anybody know how to make the night sky darker so it blends with the dark landscape?