1. A gray scale correction method for a display device which includes a color display pixel including a plurality of pixels, the method comprising the steps of: setting a target value including a target luminance and a target chromaticity of the color display pixel; measuring tristimulus values of each of a plurality of reference colors and each of a plurality of comparative colors in accordance with a prescribed gamma characteristic, wherein each of the plurality of reference colors represents a color of the color display pixel in the case where each one of the plurality of pixels has a reference gray scale and the other pixels each have a fixed pixel; and each of the plurality of comparative colors represents a color of the color display pixel in the case where each one of the plurality of pixels has an adjacent gray scale continuous to the reference gray scale and the other pixels each have the fixed pixel; finding a reference value and a comparative value from the measured tristimulus values, wherein: the reference value includes a reference luminance representing a sum of luminances of the plurality of reference colors and a reference chromaticity obtained from a sum of the tristimulus values of the plurality of reference colors; and the comparative value includes a plurality of comparative luminances and a plurality of comparative chromaticities, wherein each of the plurality of comparative luminances represents a sum of luminances of the reference colors other than each one of the plurality of reference colors and one of the plurality of comparative colors, wherein a pixel of the one comparative color that corresponds to a pixel of the each one reference color having the reference gray scale has the adjacent gray scale; and the plurality of comparative chromaticities are each obtained from a sum of the tristimulus values of the reference colors other than the each one reference color and the one comparative color; and correcting the reference gray scale based on the target value, the reference value and the comparative value.