The tesserae you choose to simulate will dictate your range of color. Marble, for instance, has soft, muted hues and sometimes streaks. Venetian glass comes in lustrous glass cubes in an almost unlimited range of beautiful colors. Another form of glass, vitreous, which is less costly, is also available in cubes in more than 100 colors. Colorful ceramic tesserae can be small or large tiles and square or rectangular, with perfectly squared corners.
Pebbles are all shapes, colors, and sizes.
The grout gives you another color choice. In early Greek and Roman mosaics, the grout was gray-beige. From the Middle Ages to the present, colored grout has also been used. Modern mosaicists often use plain white or gray Portland cement. After you have completed one cartoon, do another with the same colors of tesserae, but change the color of the grout.