In a method of operating a display device, it is determined whether an image represented by input image data is a single color image, it is determined whether the image represented by the input image data is a low gray image, compensated image data are generated by adding sub-pixel data corresponding to a color different from a color of the single color image to the input image data when the image represented by the input image data is the single color image and the low gray image, and an image is displayed based on the compensated image data.