Problem with RGB Curves fast answear plz

Support Compositing and Post Processing
1

As you can see the RGB Curves alter my background light… how the hell do i fix so it ONLY alters the mesh thats on that layer?

Using Blender 2.5



2

by using renderlayers. Here’s a tutorial:
http://www.blenderguru.com/introduction-to-the-compositor/

3

…or mask it with object ID.