A substrate for use in a display panel includes a transparent substrate and a light blocking layer which includes two layers of different optical densities. A low optical density layer that is one of the two layers of different optical densities which has a lower optical density is interposed between a high optical density layer that is the other one of the two layers which has a higher optical density and the transparent substrate. The sum of the optical density of the low optical density layer and the optical density of the high optical density layer is not less than 3.0. According to the present invention, a substrate which includes a low-reflectance light blocking layer is provided, the substrate being suitably used as a color filter substrate of a display device which has a low reflection structure, such as a low reflection film.