from a color state different from the color state of the group of particles the term u201c viewing side u201d in the present application refers to the first surface in a display layer where images are seen by the viewers the electric field threshold is either an inherent characteristic of the charged particles or an additive induced property in the former case the electric field threshold is generated relying on certain attraction force between oppositely charged particles or between particles and certain substrate surfaces in the case of additive induced electric field threshold a threshold agent which induces or enhances the threshold characteristics of an electrophoretic fluid may be added the threshold agent may be any material which is soluble or dispersible in the solvent or solvent mixture of the electrophoretic fluid and carries or induces a charge opposite to that of the charged particles the threshold agent may be sensitive or insensitive to the change of applied voltage the term u201c threshold agent u201d may broadly include dyes or pigments electrolytes or polyelectrolytes polymers oligomers surfactants charge controlling agents and the like additional information relating to the threshold agent may be found in u s pat no 8 115 729 the content of which is incorporated herein by reference in its entirety this example is demonstrated in fig2 the black particles 22 are assumed to have an electric field threshold therefore the black particles 22 would not move to the viewing side if an applied electric field is lower than the electric field threshold.