Selection effect on WPF 3D model

Thanks for the response Charles (love your WPF 3D book by the way -- very helpful!)

I have tried your suggestion but I get an error when I try to change the EmmisiveMaterial brush upon selection:

"Cannot set a property on object 'System.Windows.Media.Media3D.EmissiveMaterial' because it is in a read-only state."

Any ideas on how to fix that?  Also, if my other materials for a piece of furniture are mostly white, will I notice the effect created by the EmmissiveMaterial?

It seems like this sort of thing (selection effect) would have been solved many times over by other people already but I'm having no luck finding anything.

Many thanks for your help,

Mike.