Here's an update on my current painting project:
I added more drips of paint in different directions, a sheer layer of a gray-lavender color to what should be the land/water part of the map, and an opaque violet octagonal border to represent the Beltway. I think I am going to go in to the black metro rail system and make parts of it opaque again and even add some highlights. This way there will be even more depth and the rails will look "pipe-like." I should be done in a few days.