We used an improved cothermal evaporation route for the first time to achieve quaternary semiconductor nanostructured alloys, using an example of Zn(x)Cd(1-x)SySe(1-y) nanobelts. The PL (bandgap) of these as-grown nanostructured alloys can be continuously tunable across the entire visible spectrum through experimentally controlling their compositions. Such widely controlled alloy nanostructures via composition/light emission provide a new material platform for applications in wavelength-tunable lasers, multicolor detectors, full-spectrum solar cells, LEDs, and color displays.