Toner Display is based on an electrical movement of charged particles in the air space. Two type of positively charged color and black particles with different amount of charge to mass ratio and negatively charged white particles are enclosed in the toner display cell. The particle movement is controlled by the external electric field applied between two transparent electrodes. The smaller charged black toner is collected to the electrode by an application of changing voltage slowly, and black solid image is displayed. The toners can be put back to the counter electrode by applying a reverse electric field, and white solid image is displayed. The yellow toner is collected the electrode by applying a reverse electric field, and yellow solid image is displayed. Yellow, black and white images are displayed by an application of voltage in the one pixel.
Takashi Kitamura, Muneharu Takeuchi, Sakiko Nakamura, Nobukazu Miyagawa, "Control of Particle Movement for Color Toner Display" in Proc. IS&T Int'l Conf. on Digital Printing Technologies and Digital Fabrication (NIP23), 2007, pp 633 - 635, https://doi.org/10.2352/ISSN.2169-4451.2007.23.1.art00030_2