[DanLevin247]

Here's the deal...you can do this "color change glass" easily. You just have to look at it from an idiot's point of view. A bucket of black paint with a device to make it pour evenly across a plane is mounted directly above a plane of glass. When a button is pressed the paint is poured onto the window. To undo this painting, the same process is applied with paint thinner. Voila. Color change glass