Quote - I believe you are confusing outer and inner with exterior and interior.  Outer refers to the edges of a sphere, for example, which are moving away from the camera. Or facing away from the camera.  Inner is the surface closest to the camera, or facing the camera.

Yes, I think so too. So let's take a balloon as an example. The outer color would be the inside surface of the balloon that faces away from the light, and the inner color would be the outer surface facing the light?

Or the outer color would be the back face of the ballon that's on the far side away from the light source, and the inner color would be the forward face of the balloon that is facing the light source?

Or both? :)