A "smart" soft membrane exhibiting controlled multistructural color has been synthesized by the mechanical immobilization of a single side of a polymerized nonclosest packing colloidal crystal. A tapered gel with one fixed surface on a gel-bond film reveals monostructural color. After a partial hydrolysis of the gel to change its volume from the original size, the structural color varies depending on the thickness of the membrane. The tone can be tuned by simply changing the composition of the mixed solvent.