Spatially resolved laser micro-annealing (process shown on inside front cover) has been used to drive an amorphous to nanocrystalline phase transition in Si inverted colloidal photonic crystals to create micrometer-sized refractive index patterns (observed as the yellow color in the Figure). This provides a simple means of tailoring the optical properties of Si photonic crystals, and has applications in photonic crystal miniaturized optical components, devices, and circuits.