Quick overview
Using CTG layers will allow you to fill closed areas in an instant:
This tool is made for the lazy! You won't need to set several parameters for the color to be spread to the outline, or filling holes (have fair expectations though).
You can even, colorize two (or more) areas with a single stroke, even if they are not in contact, and without filling the gap between them either:
On this frame of the Decor_interieur project, the Squiggle which was meant to colorize the paper did, by extension, 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. You will learn how to Extract colors with Antialiasing in the following pages of the manual.