如何使用数据触发器更改WPF窗口背景？

I want to change the background color of our apps main window when a property changes. We have a business date that can be changed and I want to change the window background when it has changed from expected. I've set up a property to tell this. But can I set a style datatrigger on a window that changes itself? Or would I need to do this in the app.xaml? I want to change the background color of our ap