Torch fire one or more light coats of colored transparent enamel on the disk until achieving the color you want.
Note: If you find the colored transparent enamel is too dark and hides the texture, use a mesh size sifter with smaller holes. I normally use an 40-mesh sifter for enameling; however, I often use a 150-mesh sifter for this step. In my opinion the layer of color sifted through the 150-mesh sifter is less intense in color due to the smaller grain size and it looks lighter. If the color is too light, I can always add another coat.
If the edges of the disk are rough, use an alundum stone, file or sand paper to smooth them. This will also help prevent chipping.