Can’t add materials to importeI just imported an .fbx file from mixamo and try to apply textures myself.
If I go for the whole workflow they have on their site my animations have weird holes in the textures.
The problem I have now is that I can’t add the materials to the mesh.
There is also no “Add material” option like I saw in some tutorials. I used the standard import options for the .fbx.
Got the same problem.
Its not possible to add a material to a mesh if you imported a mesh without embedded materials.
Would like to get a answet too if there will be a way to do it.
press on the object from the library once that window opens click on the add material and then go to the preview window grab the material drag and drop on the object 
Thanks a lot! I had the same problem and your solution has worked perfectly.
