Close-packed and non-close-packed colloidal photonic crystals of silica spheres have been imaged in real space to reveal their 3D structure. Although the lattice spacings are of the order of a micrometer, these crystals can also be characterized in reciprocal space using small-angle X-ray scattering (see figure). After infiltration with silicon (see inset), the internal 3D structure of these photonic crystals can only be probed using X-ray scattering.