Design-time-only background color in WPF?

Question

In WPF XAML there is the convenient DesignHeight and DesignWidth, for instance in code as

Answer 1

There's an undocumented property d:DesignStyle of type Style that you can set on a user control. This style is only applied in the designer and is not used at runtime.

You use it like this:

Or like this:

Note however that any value set on the Style property (the one used at runtime) will also override the DesignStyle in the designer.