WinRT apps check if the Windows theme is set to dark mode through IUISettings3::GetColorValue().
An option needs to be added to Winecfg to enable dark mode support, which just sets the registry key AppsUseLightTheme to 0 for dark mode and 1 for light mode. It will have to be in a separate merge request. Also, not sure if a dark mode checkbox should be added or if dark mode should be automatically set based on the loaded theme in Wine. Though, for the latter there needs to be a property that returns the mode of the theme. Name alone might not be sufficient.
Marking this as draft because I'm not sure what I'm doing wrong with the test. It's returning E_NOINTERFACE for IUISettings3.
-- v2: windows.ui/tests: Add IUISettings3::GetColorValue() tests. windows.ui: Implement IUISettings3::GetColorValue(). windows.ui: Add IUISettings3 stub interface.