Materials greyed out in Material Manager

Hi.  Can anybody explain why certain materials are greyed out in the Material Manager window?  I’ve attached a screengrab showing that the “Sodalime,”“Concrete 01,” and “Metal - Rusty Steel” materials have a light grey overlay.  The “Metal - Rusty Steel” material, for instance, is part of the Broadcast collection of materials.  I’ve used it before, but never seen it load with the grey overlay.

Thanks so much!

Mark