Disclosed are pigment particles prepared by a process which comprises (a) preparing a solution of a polyalkylene oxide compound in water; (b) preparing a solution of a cationic dye in water; (c) admixing the solution containing the polyalkylene oxide compound with the solution containing the cationic dye to form a mixture; (d) adding to the mixture a solution containing a heteropolyacid in water, an alcohol, or a mixture thereof, thereby resulting in formation of pigment particles having an average particle diameter of no more than about 300 nanometers; and (e) after addition of the heteropolyacid to the mixture, neutralizing the mixture by addition of a base. Another embodiment of the present invention is directed to an ink composition comprising water and the aforementioned pigment particles.