In my A/C builds I lay a clear opposite in base to my highlighter meaning if I use Tamy panel wash then I lay down an acrylic base of clear gloss this allows the wash to only go to the recess for the most part in crevices only.The wash is then lessened if desire by a white thinner something relatively weak streaks can be pulled due to the gloss.The final coat is up to you flat or semi I only use chalks/pastels(avoid oil base pastels) on a flat surface sticks much better.That's Me others may vary mind you I still have fear of ruining a build in the final stages.