[Dark Mode] MonthCalendar/DateTimePicker is not in drak mode after enabled SystemColorMode.Dark

[Olina-Zhang]

.NET version

9.0.0-rc.1.24418.2 + private dlls built from winforms repo main branch

Did it work in .NET Framework?

No

Did it work in any of the earlier releases of .NET Core or .NET 5+?

This is a new feature Dark Mode: #11857

Issue description

MonthCalendar/DateTimePicker is not in drak mode after enabled SystemColorMode.Dark

Steps to reproduce

1. Create a WinForms .NET application with MonthCalendar/DateTimePicker control
2. Enable DarkMode by Application.SetColorMode(SystemColorMode.Dark) in Program.cs file
3. Run application to observe

[ssflynn77]

I could be wrong but it looks like this is a deeper issue with Windows Desktop 9 ignoring colors for DateTimePicker:

https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.datetimepicker.calendartitlebackcolor?view=windowsdesktop-9.0