Structural colored balloons (SCBs) consisting of polystyrene microcapsules in water were prepared and characterized. SCBs were produced by the solvent evaporation method of W/O/W-type double emulsion. Because the surface thickness of SCB was controlled to be comparable to a visible-light wavelength, SCB developed various structural colors from violet to red depending on the surface thickness. SCB characterization revealed that (1) the surface thickness was independent of SCB size, (2) the developing color distribution was random, and (3) the surface thickness was strongly related to the developing color. The relationship between surface thickness, developed color, and capsule size can be predicted by an optical theory. Scanning electron microscopy (SEM) images proved the validity of the theoretical calculation.