The trick I use is:
- Go in map, open F11 (if you have it),
- Open the SimObjects menu and click Sky,
- Press F3 and open the fog section,
- Make the fog really dark, and color it about the color of the horizon of the sky, but a bit more black,
- Make the fog distance around -200 (you must put a - or else it doesn't look right),
- Hit apply. Open the Sun tab under SimObjects,
- Change the hue and saturation to something dark, like 0.1 0.1 0.2 and 0.2 0.2 0.3 (the last number should be 1 higher or else it will look ugly)
- Hit apply.
- ???
- Profit.