Poly(o-toluidine) (POT) was synthesized via electrochemical polymerization on a flexible indium tin oxide sheet using two supporting electrolytes: sulfuric acid (H2SO4) and 1-butyl-3-methylimidazolium chloride (BmimCl). The coloring response time and efficiency were investigated with respect to polymerization time, electric field strength, H2SO4 concentration, and types of electrolyte solution. In addition, the cyclic voltammetric study of POT was studied in the potential range between -1.0 V and +1.5 V vs. Ag/AgCl. The synthesized POT displayed many distinct colors: colorless in the fully reduced form; yellow in the reduced form; green in the intermediated form; and blue in the oxidized form. With increasing applied electrical potential and acid concentration, the response time for the color change of the POT films became increasingly shorter. Perchloric acid provided the shortest response time due to its high dissociation constant value. The optimum response time was within 6 s for the coloring change from blue (oxidized form) to colorless (reduced form), under the testing conditions of 1.0 M H2SO4, 3.0 V. The response time for POT synthesized in BmimCl was longer than that of POT synthesized in H2SO4. However, the additional advantage of using BmimCl as the supporting electrolyte was to provide a smooth POT film surface. (C) 2016 Elsevier B.V. All rights reserved.