How can I adjust the sky color without changing the lighting?

I am using Cycles. I have a lighting arangement that works fine for me, but the background sky color is too dark. I would like to adjust that color, without having it affect the lighting in the scene. How can I do this?

Try adjusting the ambient occlusion in the ‘world’ tab. I am afraid I do not know exactly what this does but for me it seems to stop the background colour affecting the mesh(es).
I hope this helps.

try this. I think it will help. green is background.