Texture painting not applying to selected layer, thus screwing up my base colors.

I am trying to make a cartoony game character, so I have a base color, and I want to paint in my AO and lines on a new layer using multiply. However, even though I have my darkness layer and image selected, painting in the 3D view results in the paint being applied to my base colors. I need it to be applied to my darkness layer.

If I paint in the UV image editor, everything works correctly. Its only when I paint in the 3D view that it has this problem. Is there some way to sync it so that whatever image I have open in the UV image editor, is the image that will be afected by texture paint in the viewport?