Abstract: A colored photomask has a glass substrate with a masking film deposited thereon formed of a non-stoichiometric chromium oxide composition produced by heating chromic oxide or metallic chromium in a clear oxidizing atmosphere of oxygen or an oxygen-nitrogen mixture at a total pressure of 0.5 .times. 10.sup.-.sup.4 to 5 .times. 10.sup.-.sup.4 Torr and at an oxygen pressure of 0.1 .times. 10.sup.-.sup.4 to 5 .times. 10.sup.-.sup.4 Torr to generate the vapor from the chromic oxide or metallic chromium, and depositing the rising vapor onto one surface of the glass substrate heated and positioned within the oxidizing atmosphere in a manner similar to a known vacuum-plating process, and at least one window in the masking film formed by etching the film.