No "Material" attribute for 3D Solid

Hello,

I imported a block reference from an outside source, and I need to apply a material to it. I can apply the material to the reference, but it does not render. When I double click on the block and try to edit the 3D Solid inside, there is no "Material" attribute under the 3D Visualization section of the Properties window. (See attached screenshsot)

What can I do?

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