Abstract: Applicants have discovered a new type of optical switching and display device using an active layer comprising electrochromic protein. In essence, the device comprises a cell composed of an electroded back wall and a transparent front wall including a transparent electrode region. A film comprising electrochromic protein is disposed between the two electrodes. In the absence of voltage between the two electrodes, the film reflects light of a first color. If a voltage is applied, the color of the reflected light changes. Because the device uses reflected light rather than transmitted light, backlighting is not required, and the device is highly efficient as compared with conventional LCDs.