Magnetic field is an effective stimulus to assemble magnetic colloidal particles into ordered structures that can display field-responsive photonic properties. Magnetic assembly thus represents a powerful method to produce novel photonic materials with wide applications ranging from various types of color displays to chemical and biological sensing devices. In this article, we review several recent examples of magnetically induced assembly of colloidal particles into photonic structures that show responsive visible-light diffractions. For each case, we discuss the mechanism of assembly and the control of the photonic properties, as well as the advantages and limitations for potential applications.