如何从XAML设置WPF usercontrol属性？

I'm trying to set the fill property of several instances of the same usercontrol from XAML in order to distinguish them. I'm using a dependency property in the C# codebehind of the control and referring to that in the XAML when I instantiate the control. Here's a simplified example of what I've tried, first the XAML of the user control:I'm trying to set the fill property of several