 The history of coloration goes back to 1704 when Diesbach discovered Prussian blue (hexacyanoferrate), which changes the color from transparent to blue under oxidation of iron.In the 1930s, Kobosew and Nekrassow first noted electrochemical coloration in bulk tungsten oxide.While working at Balzers in Lichtenstein, T. Kraus provided a detailed description of electrochemical coloration in thin film of tungsten trioxide (WO3) on 30 July 1953.