From Xojo Documentation
| This item was deprecated in version 2019r3.
Please use Color.IsDarkMode as a replacement.
Indicates if the app is running in dark mode for the OS.
result = IsDarkMode
|result||Boolean||True if the app is running in dark mode and False if it is not.|
Currently this will only return True when running on macOS Mojave or later when dark mode is enabled in System Preferences and when Supports Dark Mode is set to ON in the project Shared Build Settings.
For the most accurate results, IsDarkMode is not cached. If you are using it within a tight drawing space (such as Listbox rows) you may optionally cache it yourself for faster drawing.