A rainbow pen! Hold down the mouse to draw a disappearing line. Change the "Colour Change Time" variable to change how frequently the colour of the pen changes. Change the "Tail" variable to determine how long the line behind the pen goes.
I used cloning to make the line behind the brush. Try setting the colour change time anywhere between 0.2 and 0.5. It has a cool effect! So why didn't I use graphic effects? It's because they lag.
