Getting started

1. Install the zip: Edit ▸ Preferences ▸ Add-ons ▸ Install from Disk, then enable Material By Collection.
2. Select a collection in the Outliner and open the Material tab of the 3D Viewport sidebar (press N).
3. Pick a Material. Every mesh object in the collection takes it.
4. Clear Override puts each object back on the material it had before.

Slot chooses which material slot is written on each object. Include Sub-collections applies the override to nested collections too; a sub-collection can opt out with Exclude from Parent Override. Enter Collection Instances reaches the geometry inside collection-instance empties.

Open Collection Manager (Ctrl+M) shows every collection at once, with a search field, Sync All and Clear All. A warning icon marks a collection whose objects are out of sync; Sync Now re-applies its material.