You will see that filling is done in an instant, like a magic trick.
This tool is made for the lazy ones !
You won't need to set several parameters for the zone to be spread to the outlines, or fill the holes (wherever reasonable, obviously).
You can even, with one stroke, colorize two zones (and even more), even if they don't touch each other, and without filling the gap between them either.
On this background below, the Squiggle that was meant to colorize the paper did, by extenison, colorize all of the desk, including the books, the lamp, pencil box that were close.
You will need to chose other colors and draw Squiggles on the desired zones to fill the surrounding objects.
It is important to notice that the color, even if it correctly fills the zone whatever the shape of your stroke and/or its opacity, will not be antialiased. See further in this lesson how to Extract colors with Antialiasing.