An electrochromic device (10) of reversible light-transmissivity comprises a pair of spaced-apart window plate members (11, 13) bearing electrically-conductive surface layers (12, 14) and containing an electrochromotropic electrolyte solution in the intervening space (16). The electrolyte comprises an aqueous inorganic solution of a silver salt and may further comprise a salt of a transition metal. The electrolyte solutions are responsive to varying applied voltages by transitioning between solution phases of varying light-transmissivity which, depending upon solution composition, may be persistent or passively reversible.