-3.5V that transmission is suppressed in the range of 500 to 700 nm. Also, from the color wheel we can say the counter colour of most suppressed colour in transmission spectra will be the colour of the film\[29\]. The simple analysis of UV-Vis spectra allows one to understand the origin of the color appearance of the electrochromic device. This also may enable one to understand that % T corresponding to a given wavelength may be tuned by appropriately enhancing/suppressing the %T spectra at other wavelengths. Relative %T corresponding to different wavelengths decide the exact colour of appearance and can be obtained from CIE (Commission Internationale de l’Eclairge International Commission on Illumination) color calculator (Osram Sylvania\[30\]).

Figure 3 shows the CIE color calculator chart with the photograph of our actual devices with different applied bias. The CIE color calculator has been used here to calculate CIE coordinates corresponding to the device appearance color for a given applied bias. Initially at zero bias (OFF) device is transparent hence it allow the white light to pass through it\[31\]. As the applied bias voltage increase, only blue color spectrum pass through it as compared to green and red. According to colour appearance, related point 