Well, after a bit of experimenting I think I've finally hit on some techniques for camouflaging aircraft with Inkscape. The picture below shows one attempt. You draw out the shape, fill it, color the outline the same as the fill, then use the blur feature on the lines to make the sprayed-on look. You should make the outside edges of your piece slightly larger than you really want them to be - for a good reason. After you have the camouflage approximately like you want it (and it's WAAAY easier to do with the bezier curves than what I've been doing in GIMP (Which BTW is still a good program)) then you duplicate the pattern piece and use the move object and down features to move the duplicate to the top. Then, you can use the "clip" feature (See above) to clip off the offending edges and conformn the camouflage to your part. Then you can delete the duplicate pattern piece, and the blurred edges only exist where you want them!