I dont know about you,
but i think many rFactor tracks use way to blue ambient colours.
Here´s a little comparison:
Now of course this is a very difficult subject, as tastes are different.
But i prefer a rather neutral look, as it seems more realistic to me.
You can find the RGB values youre looking for using photoshop or a similar program.
Ambient settings can be changed in your track´s gdb file.
I used DayAmbientRGB = (90,90,90)for the pics above.
Remember, changing such things can cause mismatches.
So always make a backup of the original file.