Standard MacOS Aqua light window appearance. This is the typical way to run Plaque Simulator.
MacOS 10.14 (Mojave) introduced a dark window appearance option. If you are running MacOS 10.14 or later you can experiment with system wide dark mode by selecting dark appearance in the MacOS System Preferences General pane. Irrespective of your system appearance setting, you can run PS6 in either light or dark window appearance using the buttons in the MacOS Appearance group of the Colors preference pane. To remember this preference settings for subsequent launches be sure to click the Save Preferences button.