In this letter the authors present both experimental and numerical studies of the optical properties of four-layer artificial opals. The stacking of four layers of spheres may arise according to three different arrangements: face-centered cubic, hexagonal close packed, or double hexagonal close packed. The study shows that the transmission spectra features are characteristic of the type of stacking, and thus, each color region observed under the optical microscope can be unambiguously associated with one of the stacking types.