The properties of electrochromic molybdenum oxide (as a thin film) has been adjusted by incorporating the oxides of Co, Cr, Fe, Ni, W or Zn; films were made by cathodic electrodeposition. The deposition solutions employed were prepared by dissolving powdered molybdenum metal in hydrogen peroxide solutions. Such films were robust and showed a good contrast ratio. Addition of other metal salts to the deposition solution allowed mixed-metal oxides to form. Further "fine tuning" of composition and hence properties is possible since the ratio of constituent atoms in solid films is a function of the potential employed for deposition. Some of the mixed-metal oxides evinced an extended electrochemical "potential window", since the onset of gas formation is suppressed during reductive electrolysis. All films evince a relatively slow electrochromic transition. A correlation is shown between shifts in optical bands and the (logarithm of) chemical diffusion coefficient for the proton through the film which is taken to infer ion motion proceeds via a hopping mechanism.