We prepared solid-state electrochromic (EC) cells based on phthalate derivatives and containing a gel electrolyte. The cells showed vivid color changes via electrochemical reactions, i.e., from being water transparent to assuming one of the three primary colors (cyan, magenta, and yellow). Moreover, we obtained continuous-tone images by using the three primary-color EC cells. The formation of continuous-tone images by using the EC cells was realized by applying a rectangular-wave voltage with various duty ratios. In addition, according to a subtractive color-mixture process, we obtained multiple color representations, including intermediate red, green, and blue colors, by stacking two of the three primary-color EC cells.