The Invantive products for Microsoft Windows render their windows light or dark, following the app mode set in the operating system itself. The appearance is established once, when the product starts: a change of the operating system setting made while a product runs is not followed, because windows fix their colours as they are built. The following environment variable controls the appearance and is available on the GUI products from release 27.0: - `INVANTIVE_APP_THEME`: overrule the appearance in which the user interface renders. Defaults to the app mode of Microsoft Windows, and to light on an edition or version which does not have that setting. The value is one of the following and is not case sensitive: - `Light`: render light. - `Dark`: render dark. Any other value is ignored, upon which the app mode of the operating system decides after all. The variable is meant for support and for reproducing a problem in the other appearance; it is not a substitute for the OS setting, which the products otherwise follow.