Monodisperse polystyrene particles with a diameter of ca. 100 nm have been coated with 8 nm shells of poly(3,4-ethylenedioxythiophene) (PEDOT) and self-assembled into crystalline colloidal arrays (see Figure) with an observed stop band in the visible regime. These materials could be used in developing photonic crystals with frequency-and dopant-dependent optical properties.