Both linear-and nonlinear-optical properties of Bu4N[Pt(L1)(L2)] (1; L1 = [4',5':5,6] [1,4]-dithiino [2,3-b] quinoxaline-1', 3' dithiolato; L2 = (R)-alpha-MBAdto dithiooxamidate, where (R)-alpha-MBA = (R)- (+)-alpha-methylbenzyl) upon HCl addition at room temperature change dramatically: the color turns from deep blue to green; the luminescence switches from deep red to green; the nonlinear-optical response (first hyperpolarizability) increases by a factor of 12. Thus, 1 behaves as a unique multiresponsive optical switch whose properties can be followed by the naked eye.