And one more tip... washes aren't for accenting the surface details. The technigue is for imitating of gathering of a dirt in all apertures, slots etc.. To make someting bulge on a surface it is used the rule that all what is closer to a looking man has to be lighter and all that is farther from the guy has to be darker. In other words, if your surface is yellow ( like it is now ) all rivet heads have to be of a slightly lighter yellow colour than the surface one is.
In my opinion the way you should use for making the rivets accented is....
1. stick all rivets and panels to the wing.
2. spray the entire wing surface with the yellow.
3. dry brushing of rivet heads with the yellow of lighter tinge.
4. applying a dark wash in order to replicate of gathering of dirt around rivet heads and all apertures, slats, wiping off of the wash excess.
5. spraying of another but very, very thin layer of the base yellow colour. But it is unnecessary if you are satisfied with the final effect.
6. spraying of the clear protecting coat.