In the present study, we demonstrate the precise tuning of surface plasmon resonance over the full visible range by compositional variation of the nanoparticles. The addition of sulfide ions into the Au@Ag core-shell nanocubes generates stable Au@Ag/Ag2S core shell nanoparticles at room temperature, and the plasmon extinction maximum shifts to the longer wavelength covering the entire visible range of 500-750 nm. Based on the optical property, the Au@Ag core shell nanocubes are employed as a colorimetric sensing framework for sulfide detection in water. The detection limit is measured to be 10 ppb by UV-vis spectroscopy and 200 ppb by naked eyes. Such nanoparticles would be useful for decoration and sensing purposes, due to their precise color tunability and high stability.