Molecular or supramolecular systems capable of electro- and photostimulated color changes are still rare. We present a device design based on an electrostatic complex of a nanoscopic polyoxometalate cluster and a polyelectrolyte. The coating reversibly chances color front transparent to blue by photo- and/or electroinduced stimulation. The choice of the components results in perfect transparency over the entire visible range, a large optical response, reversible operation, and excellent stability.