Very nice diagram, Marrin. That confirms it's a Microencapsulated Electrophoretic Display. See explanation quoted below. While the example below is for 40 micron capsules, the Seiko uses only 10 micron capsules. The basic principle is very simple: with the right charge, the black particles are brought up to the surface of display; with the opposite charge, the black particles are sunk to the bottom, while the white particles brought up to the top. That's about it.Source: https://en.wikipedia.org/wiki/Electronic_paper
"One early version of electronic paper consists of a sheet of very small transparent capsules, each about 40 micrometers across. Each capsule contains an oily solution containing black dye (the electronic ink), with numerous white titanium dioxide particles suspended within. The particles are slightly negatively charged, and each one is naturally white. The screen holds microcapsules in a layer of liquid polymer, sandwiched between two arrays of electrodes, the upper of which is transparent. The two arrays are aligned to divide the sheet into pixels, and each pixel corresponds to a pair of electrodes situated on either side of the sheet. The sheet is laminated with transparent plastic for protection, resulting in an overall thickness of 80 micrometers, or twice that of ordinary paper. The network of electrodes connects to display circuitry, which turns the electronic ink 'on' and 'off' at specific pixels by applying a voltage to specific electrode pairs. A negative charge to the surface electrode repels the particles to the bottom of local capsules, forcing the black dye to the surface and turning the pixel black. Reversing the voltage has the opposite effect. It forces the particles to the surface, turning the pixel white."