In human retina, rod cells contribute to scotopic or dim-light vision and cone cells to photopic or bright-light vision. Excitation of the cone cells leads to the perception of color while that of rod cells helps in perception of various shades of gray. At low levels of illumination, only the rod cells are excited and gray shades are perceived. As the illumination level increases, more and more cone cells are excited and actual colors are perceived. The HSV model separates out the luminance component of a pixel color from its chrominance components, which is similar to the human perception of color. Hue represents pure colors, which are perceived by the excitation of cone cells. Saturation gives a measure of the degree by which a pure color is diluted by white light. Using the results of these analyses, we determine relative importance of hue and intensity based on the saturation of an image pixel. We effectively apply this method to the generation of a color histogram where each pixel contributes to gray color and true color. Using a weight function, percentage of true and gray color contributions of a pixel are measured. This information is used for content-based image retrieval applications.