Nearly monodisperse silica spheres with a diameter of ca. 140 nm containing magnetic cores of gamma-Fe2O3 were synthesized following a similar method by Stober(1) and Philipse.(2) Rendering a structural color was successfully achieved by thorough deionization of the aqueous suspension of the spheres. The magnetic tunability of the structural color of the colloidal crystal was demonstrated. The optical property was characterized by UV-vis reflection spectra.