Colored electrophoretic displays

An electrophoretic medium comprising a fluid and first, second, third and fourth particles (1-4) dispersed in the fluid, the medium being characterized in that:

• (a) the plurality of first (1) and the plurality of fourth (4) particles bear charges of opposite polarity and each have a polymer coating comprising at least about 60 per cent by weight of an acrylate or methacrylate ester monomer comprising a hydrocarbon chain comprising at least about six carbon atoms, one of the first (1) and fourth (4) particles being a light-scattering particle and the other of the first (1) and fourth (4) particles being a substantially non-light-scattering particle comprising a pigment having a subtractive primary color selected from the group consisting of cyan, yellow, and magenta;
• (b) the plurality of second particles (2) bear charges of the same polarity as the fourth particles, have a polymer coating comprising at least about 60 per cent by weight of a polydimethylsiloxane-containing monomer, and comprise a pigment having one of the subtractive primary colors different from the substantially non-light-scattering one of the first (1) and fourth (4) particles;
• and
• (d) the plurality of third particles (3) bear charges of the same polarity as the first particles, are substantially non-light scattering and comprise a pigment having one of the subtractive primary colors different from the substantially non-light-scattering one of the first (1) and fourth (4) particles and different from that of the second particles (2), and
• wherein the yellow, magenta, and cyan pigments exhibit diffuse reflectances at 650, 650 and 450 nm, respectively, measured over a black background, of less than 2.5% when the pigment is approximately isotropically distributed at 15% by volume in a layer of thickness 1 μm comprising the pigment and a liquid of refractive index less than 1.55.