Not a tutorial, a more like a bunch of slide shows instead in which GIMP layer modes are shown, using my 2005 Holiday Splash image.
Changing the mode of the edge detected, anti-aliased, blurred and then leveled grayscaled layer over the levels adjusted original gives many different versions of the images colors. Use the mouse on the list of Layer Modes to change the Image window (javascript).


You can see all of the layer modes here, either one at a time or as a slide show. You can't see the mode name here though.