Cobalt(II) hexacyanoferrate(III, II) films show reversible electrochromic behavior in potassium salt electrolyte. Gold-covered foil was used as a conductive, optically transparent substrate onto which cobalt hexacyanoferrate films were deposited by a slow coagulation method. Both voltammetric and spectroelectrochemical results are consistent with the existence of two cobalt hexacyanoferrate forms, presumably KCo1.5II[Fe-II(CN)(6)] and K2CoII[Fe-II(CN)(6)]. The separate nature of the redox reactions of these forms is clearly evident from spectroelectrochemical measurements, particularly from voltabsorptometry, which involves monitoring of the time-derivative signal of absorbance as a function of the linearly scanned potential. Combination of voltabsorptometry with voltammetry allows determinations of molar absorptivity and film loading, and it permits changes of concentration of colored redox centers vs the applied potential to be monitored.