To get it to look realy good, just lower the car shine setting in the CFG to around 0.65-0.50 and then go into your graphics card control panel.
From the graphics card panel go to color and select color for full screen 3d, then increase the contrast and decrease the brightness.
I find that in the ATI CCC, LFS looks best if I set the contrast to 160 and the brightness to -60, any higher and the sky starts to turn into a single mass of color. Of course this will be different for everyone, so just play around with it. but make sure that you always keep the settings even, so if you go to 150 contrast, go to -50 brightness, if you don't it will either be to dark or it will go grey.
Note: any recorded footage will still come out normal contrast and brightness, it won't be corrected like you see it in game.