What is the necessary setup in case I want the light building to ignore the Skysphere

Hi guys,

I am working on a map where I altered the default sky-sphere from the default FPS Template, so the sky is really yellow (like the fire). I’ve also added a terrain to the map. The map looks perfect until I build light because after light building, the landscape becomes very very bright and yellow. It seems that my sky-sphere affects the final light of the map. Is there any way to change this? ![alt text][1]
PS Colors determined is unchecked!