The elucidation of the role that injected cations play in the creation of electrochromic (EC) color centers in hydrated WO3 films is presented. The electron and cation contributions to the lattice distortion upon film coloration have been evaluated. The evolution of the fundamental absorption edge and vibrational bands of crystalline hydrate films of the WO3 . n(H2O) (n = 2, 1/3) was monitored in situ in a spectroelectrochemical cell during the coloration process by visible and Fourier transform Raman spectroscopy. The electrochromic performance and film stability were studied using cyclic voltammetry and spectroelectrochemistry. Isotopic effects of blue shift of the fundamental absorption edge and vibrational band shifts upon film coloration with H+ and D+ cations at the same charge density have been found, The analysis of vibrational band shifts during electrochromic coloration with H+ and D+ cations indicates that along with the lattice polarization induced by injected electrons forming polarons, a strong lattice distortion generated by inserted cations is occurring as well. An explanation of the origin of the blue shift of optical gap energy upon coloration by three different effects of the electronic structure rearrangement is proposed.