How do you color a rectangle in C# that has been declared in XAML in WPF?

There is a rectangle control in XAML. In my C# code there are times in which it would be nice to fill the background color. How does one do this?

The rectangle has a text block nested inside. The Fill works to color the whole rectangle but it also blocks out the text. On the other hand, using the stroke first colors the rectangle and I can modify the enclosed test but the rectangle does not have a boarder.

I have read this solution. The way to do it might be to bind the Rectangle background colour to a property and use INotifyPropertyChanged to trigger the update of the colour based on the change.

How do I bind the Rectangle background colour to a property?