You were almost there. Use a blank QWidget as the central widget, set its background color to be what you desire. You may have to derive from QWidget so you can override the resizeEvent, but you basically want it to resize to be the same size as the central area of your main window. If you don't use Qt Designer to set up a default UI for your app, then you can configure the main window to have no status, tool, or menu bars if that's what you want.