In a display device comprising an optical region containing a plurality of pigment grains utilized for wavelength selection, anti-reflection, improvement of the light emitting performance and the like, dyestuff molecules utilized for forming the pigment grains to be dissolved in a solvent in which the dyestuff molecules are insoluble originally are chemically modified, and then the solubility of the modified dyestuff molecules in the solvent is reduced by energy transfer thereto to aggregate the dyestuff molecules, so that grain sizes of pigment grains are suitably controlled for the optical region in accordance with its use.