Materials that are skipped
Case | Behaviour |
|---|---|
Linked (library) material | Read-only, so it cannot carry the pass. Skipped, counted in the report, renders black. |
Grease pencil material | No shader AOV path. Skipped. |
Excluded material | Renders black by your choice |
Material with no node tree | Switched over to nodes so it can carry the pass. Counted in the report, because this edits the material. |
Black therefore means "not a material" — background, excluded, or skipped. That is also why no generated colour is ever black or near-black.