A system and method for improving the saturation of a red-green-blue-white (RGBW) image signal, the system including: an image signal classification unit to classify a frame of an image signal into an image classification unit using an image classification parameter based on a luminance and a saturation of the frame; a backlight luminance controller to increase a backlight luminance with respect to the frame if the image classification unit thereof is a saturation improvement target; and a W sub-pixel controller to decrease a luminance of a W sub-pixel of the frame according to an amount of increase in the backlight luminance.