A method of manufacturing a display device includes a step of forming an insulating layer on a substrate, a step of coating a first mask material on an area associated with a first color pixel on the insulating layer, a step of coating a second mask material on an area associated with a second color pixel on the insulating layer, and a step of patterning the insulating layer using the first mask material and the second mask material, and forming a first diffraction grating and a second diffraction grating that have different grating pitches. The first mask material and the second mask material are coated by a selective coating method.