An auto action I made to help fill flat colors. Start by selecting the outside area of the drawing, then play the auto action. It inverts the selection, fills the selection with color, then deselects the area. It leaves you with a solid color block to lock the transparent pixels/clip a new layer above it to fill in the colors.
If your lines aren't closed, you'll have to fill in any small areas that don't get filled.
I have it set to the keyboard shortcut ctrl+shift+F, but feel free to make it whatever you like!
