Flash Frame-By-Frame Animation: Detailed Animation Part VII

Then, to start off with, just fill in the area that you want to use a gradient on; just pick a base color, whatever your “average” color is going to be. If you’re using dark colors like I am, you may want to go back to your lines layer and change the colors of line segments in the middle of dark areas.

You'll notice that I didn't fill in my last two panels; this is because they're duplicates of a few previous panels, and when I'm done detailing those other panels then I'll just copy them onto their duplicates.