Programmable Paint

There is currently paint that changes colors when it is heated. We can program circuits to heat up wires by running electricity through it. In sense we can program the visibility of paint. With this technology we can make paintings that change colors based off of observer's interactions- say when they touch a specific part of the paint.

I can imagine a frosted window but when you wipe your hand across the window, the ice melts and you see some children playing outside or a giant crab, depends on what your message is.