WO3 thin films were deposited on indium doped tin oxide (ITO) substrates by R.F. sputtering and investigated for their electrochromic properties. Iono-optical studies were performed in a three-electrode electrochemical cell to deduce information about the intercalation kinetics. Addition of acetonitrile (AN) to the non-aqueous electrolyte is found to modify the electrolyte properties and increase the diffusion coefficient by almost two orders. The device shows a coloration efficiency (C.E.) of 46.45 cm(2) C-1 and reversibility of 98%. The variation in color with applied potential has been plotted on xy-chromaticity diagram and chromic contrast of the device has been calculated using L*a*b* values. (C) 2012 Elsevier Ltd. All rights reserved.