Monodisperse silica nanoparticles (SiNPs) grafted with well-defined and highly dense polystyrene brushes are used as building blocks for the formation of three-dimensional (3D) colloidal crystals. By adjusting the refractive indices and the density of the hybrid particles with those of mixed solvents, iridescent microcrystals were formed throughout the entire suspension which were characterised by confocal laser microscopy. These core-shell hybrid particles are not charged and the driving force of the crystallization relies on repulsive forces between the polymer brushes with high grafting density. The interparticle distance is correlated to Bragg's Law and can be controlled by manipulating the grafting density and the length of the polymer brushes. Finally, the uniformity of these unique core-shell particles was exploited to generate 3D assemblies by a rapid and simple process based on centrifugation.