1. Solid layer.
The colours indicate which laye each section sits on.
The red areas show how light areas will sit on top of the colours.
3. Basic pass.
This shows the primary colours of the image and how the light sits when in white.
Here is the image with the colours adjusted to create the right tones to highlight the lighter areas.
5. Grade Pass.
This is the final image, the gradients add to the object depth.