When it comes to computer painting, remember these rules:
Rule 1: Anything to be filled with paint must have an inner border, and an outer border.
Rule 2: outer borders cannot be inner borders, and inner borders cannot be outer borders.
A target is a good example, one with alternating red and yellow rings, with a red center dot.
--So draw a circle for the red center, then 4 more circles around it for the rings.
--now paint the center dot red.
--now try to paint the next ring yellow. You'll find it can't be done... because you need to COMBINE the outer ring of the red dot and the next outer ring. But the red dot ring is in use. .
the fix? You need an identical red dot outer ring- unpainted- to use as the inner ring for the yellow. ALL ring borders (except the outermost end ring) must be duplicated in order to be able to paint them...
And guess what SmartFill does? It automatically inserts duplicate borders and adds the paint you chose.
Try it Bert-- It actually worked for me! Draw 6 or 7 circles to make a target. Use the smartfill tool, pick red, and just click INSIDE the rings (not ON the rings) you want red. Do the same with yellow and paint the alternating colors. Voila, it'll work! And when you're done, you'll find you can click and drag each colored ring where you want. Go to wireframe mode, you'll notice every ring has it's own outlines, smartfill automatically created them.
Now I just need to experiment some more my own self!