Hi Olve - The highlights and shadows were done using a simple 6 step process:
1. Paint the whole surface the colour that you want the
rib tapes to be,
2. Mask over the rib tapes,
3. Spray the colour you want the wing surface to be (masks still on the rib tapes)
4. Lighten the wing colour slightly, then spray highlights between the ribs (again, masks still on the rib tapes)
5. Remove the rib tape masking
6. Overspray along the rib and control joins with some thinned Tamiya smoke
That’s all there is to it – it is a little intensive but I have found that doing it this way is another alternative to pre shading prior to painting the main coats .