We have evaluated the optical properties of close-packed and non close-packed colloidal crystalline arrays made of hollow polystyrene spheres. Close-packed colloidal crystalline arrays were fabricated by simple evaporation of dispersions, whereas nonclose-packed colloidal crystalline arrays were fabricated by exploiting electrostatic interactions between the spheres in aqueous dispersion. Optical properties of the arrays were estimated from angle-resolved reflection spectra. The Bragg diffraction peak of the colloidal crystalline array made of hollow spheres was of shorter wavelength than in the case of solid spheres, not only for the close-packed array but also for the nonclose-packed array. These shifts were caused by a decrease in the effective refractive index eta(eff) with decreasing particle refractive index. We have found that this relationship could be explained by the simple equation eta(eff) = n(particle)phi + n(solvent) (1-phi), where is the volume fraction of the particles, for the close-packed and non close-packed arrays. The current work suggests new possibilities for the creation of advanced colloidal crystals. (c) 2006 Wiley Periodicals, Inc.