Would there be a way to design nano particles that can somehow change the wavelength that they reflect light? This would be like a type of ink or dye that changes color as a response when the frequency of an inaudible transmission was present. So you could paint a room once and then change the color to whatever you wanted by remote control.

Since Amazon developed that hand-held electronic book that uses actual ink in its LCD and isn't backlit, this seems like it could be a possibility for walls. Only to use LCD technology would require putting up large panels, which would have seams and probably couldn't be cut to fit.

So if some kind of nano particles could be designed that are suspended in paint, you could customize the color of things with a remote control or dial.

I don't know about nano particles, but they do have LCDs now that are paper thin and flexible. So eventually you'll be able to just get a bunch of smaller lcds and glue them to your wall.

Paint that changes its colour with temperature already exists. Not even nanotech.