Something
that has grown in popularity are what is known as optical illusion masks for
control surfaces. These are applied to fabric control surfaces and then the
surrounding area is sprayed with the same underlying shade, but lightened or
darkened a bit. Once removed, they provide the illusion of depth on these
surfaces.
The instructions state that the kit's control surfaces are missing ribs and recommends sanding them smooth prior to attaching these masks. I'm going to jump out here and state that were I using these, I'd remove the small areas and then place the outline mask in place prior to misting on the darkened shade.
I have seen these used and the effect is worth the effort. If you wish more in depth instructions, visit the web site link below.