I modified the script quick-sketch.scm of tuxcomputers, so it does not transform the image into grayscale, but leave the image in RGB mode.
The location of the script is "Script Fu / Artistic / Quick Sketch RGB"
This script turns a photo into an image that looks like a sketch. Clicking on the photos below will take you to larger versions.
Unless otherwise noted, the rights for the individual plugins are with their respective authors. Logo image by Jakub Steiner.