Test if Windows is using a dark theme (from a Windows forms app, for example) (This is not battle-tested in the wild)

WindowsIsUsingDarkTheme.cs

//using Microsoft.Win32
public bool WindowsIsUsingDarkTheme()
{
	var keyName = @"HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Themes\Personalize";
	var valueName = "AppsUseLightTheme";
	var value = Registry.GetValue(keyName, valueName, null);
	if (value == null)
	{
		return false;
	}
	
	if (int.TryParse(value.ToString(), out int result)){
		return result == 0;
	}
	
	return false;
}