It's not really a programming question, but it's a quick one so let me answer that. MySQL Workbench's themes are a collection of colors for certain main parts of the application. It is planned to allow customizing them in a later version. In order to get a dark theme as one of the templates please file a feature request at http://bugs.mysql.com. But keep in mind, not every UI element is colored according to the Workbench theme, e.g. text boxes still stay white as they use the Windows standard colors.