[![Trying to create a bookcase with books that have a mix of ][1]][1]
I have constructed a mesh 'bookcase' with many books on many levels. My ultimate aim is to export the bookcase and all books as a single mesh. However, I would like to ensure that my book spines have a healthy amount of color variation (as pictured).

Inside blender this is easy. I ensure that the material has an Object node (Random Object plug) that drives a color-ramp that chooses from appropriate options along the ramp.

But this is ultimately for OBJ export. So I just need standard PBR materials with no tricks.

I would like to take all the little book meshes and divide them into groups. Then I would make a single material for each collection of random books and join them into a single mesh.

I hope this makes sense. I would love to speed the creation of these assets and am sure there is some selection magic that can do it, but I have yet to figure it out.

Thanks in advance for your attention.

Follow-up: So far, my best strat is to hide everything and then do successive 'random selects' until I have manually broken out meshes that way. This is doable, but I'll still hold out hope for a more elegant solution.

  [1]: https://i.sstatic.net/EgC2b.jpg