In this video, I used dynamic painting to track a "wand" as I draw the Disney Channel logo. I used a high-visibility pen as the wand, then tracked it in Blender, and used the tip as a brush for a canvas.
I then traced the drawing and used shape keying to turn the haphazardly-drawn logo into one that was more accurate.
In this video, I modeled a spatula from my kitchen and then replaced the real spatula with my CG model. This then went to a canvas and, again, used dynamic paint to draw a message on my wall.
I achieved a multicolor effect by using the paint as a mask over a rainbow pattern -- the paint slowly revealed the invisible rainbow pattern.