Selection effect on WPF 3D model

I have a Viewport3D with multiple ModelVisual3Ds, each representing a piece of furniture in a room.  When the user clicks on a piece of furniture I want to make "select" it by highlighting the model.  I have the hit testing working fine I just can't figure out a good way to change the ModelVisual3D (or underlying GeometryModel3D) to render a decent selection effect.

This application is port from a managed DirectX app.  In the DirectX version I used a simple shader (Direct3D.Effect on the mesh) to increase the blue value of each pixel -- the result was a blue-highlighted piece of furniture.

Any suggestions on how I can create a similar effect in WPF 3D?

Many thanks for your help,

Mike.