When I showed my first version of the Glass plugin to the coder that thought it impossible, I got some words of praise but she claimed a user-selectable colored rim (like some Flash version had) was still impossible. Robert Graves did not write:
"User selectable colours?" "Mostly nameless colours, Colours you'd like to see; but one was puce Or perhaps more like crimson, but not purplish."
A stack of semi-translucent images can produce even the color #4E1609 (puce) but let’s look at the simpler example below, the color #FFAA33.
If you think about it, for any color, three layers are enough and the opacities stays within [0,1]. So with eight rim images, one for each RGB color combination, a user-selectable colored rim can be created. Try for yourself.