Here's something you might want to try......After you paint the base coat, and it's completely dry, brush or spray a coat or two of Future floor finish. This will protect your initial paint job. then, when that's dry, make a wash of a dark color, black, charcoal gray, or a brownish black acrylic - a couple of drops of water to a puddle of color, and a drop or two of liquid dish soap - This will improve the flow and help you remove the excess. Take a soft brush and slather this mixture all over the surface and into panel lines and details. I do this one section at a time, and let it dry for a bit - not too long! Then, take a slightly damp paper towel or a 'baby wipe' and start wiping the excess away, from back to front. You can use a q-tip to get into tight areas too. You can build up layers until you like the result. You can also dry brush some of the original color on top, or a lighter shade to pick out details. When you're satisfied, give it a coat of your favorite clear flat to seal it. This really needs to to be sprayed, because brushing it on will disturb the weathering. I know because I completely ruined a model that way! .......Make sure you mask off the clear parts first!