A multiple-colored electrochromic composite film of polyoxometalates (P2W18) and poly(hexyl viologen) (PXV) is fabricated by layer-by-layer (LbL) self-assembly method. The P2W18/PXV composite film exhibits a linear increase in film thickness with assembly processing, and undergoes a colorless to blue to violet transition over the potential range from +0.1 to -0.9V. The optical contrast, response time and stability for the as-prepared films are carefully investigated. These results show the validation of an LbL method based intermixing strategy for the design of tunable-color electrochromic thin films. The composite film can also be used as a pH sensor because of the pH dependence of its electrochemical response. (C) 2008 Elsevier Ltd. All rights reserved.