US Patent 7619609 Fluidic display apparatus

A display device uses the presence or absence of a pigmented fluid in a pixel to indicate pixel state. Fluid flow to or extraction from individual pixels is controlled through manipulation of row and column fluid pressures. A pixel wall opposite a viewer may be provided with a background color contrasting the color of the pigmented fluid. When present in the pixel, the pigmented fluid obscures the colored wall of the pixel, and viewer sees the pixel as the color of the fluid (a first state). When the fluid is absent from the pixel, the viewer sees the pixel as the color of the wall of the pixel (a second state). When partially present, the fluid color and the wall color mix to provide grayscale display.