I posted this in the CGTalk forum for Blender but have yet to get a response.

So I thought Id ask here.  Any help on this is appreciated guys.

I have a very simple scene where a glowing ball of light travels into the scene, over the camera (which is tracking it) and into the distance. 

My node set up (as pictured below) is two render layers. 
The base layer contains the scene and the object within the glow, in this case a simple black square, and a green plain object to serve as the ground. The base layer Include settings (pictured) has all options checked except zmask, neg and All Z. Visible layers 1 and 6 are selected. Scene Layers included in the Render is only the 1st.
The glow layer contains just about everything else, being the glow object itself (a copy of the black square given a different material), all lights (two points and a sun), 6 area lights parented to the glow object. The glow layer settings (not pictured) Include are zmask, solid, halo, ztransp, edge, strand. The zmask layers selected are 1 and 6. The Visible Layer selected are layers 1 and 6. Scene layers included in the render is just layer 6.

My problem concerns the actual compositing of the two layers together. When the actual compositing gets done my sky darkens preceptively. I can only think Ive done something wrong in my node set up (which works perfect for the glow effect i want) or that I need to disable sky in the base render layer, create a third RL and enable ONLY sky for that layer and then mix it in to the node set up (or would I use an Alpha over for that?)