Here's the first step. I've sketched the inside edges of the canopy and the KC-135. Since watercolors are, for the most part, transparent, you can't cover one color with another the way you could with oils. Sometimes that's a good thing, and sometimes it's not so good. When I want a definite edge between colors, I use masking tape to keep paint off an area.
Now I'm ready to paint in the sky above the tanker.