It does not fall through to the underlying PolyCollection3D?

I think that's part of what @oscargus is trying to do in #23914?

@tacaswell Poly3DCollection makes no references to cmaps whatsoever, relying on the higher level functions to call the map to get facecolors.

In fact the light source shading itself is even done in voxels as well.

The data for voxels is fundamentally binary (show this voxel or don't) and so don't map onto a cmap.

Granted, the cmap kwarg is passed down the chain all the way to Collection and it is not an exception to pass one, but there is not data to evaluate that cmap at. voxels does not accept a c or colors argument (though that may be a reasonable addition which would make the handling described by the current docstring necessary)

For reference, I noticed this while looking into #24277, where the reporter is requesting pretty much exactly that. its easy enough to work around with the tools provided, and bringing in norms and all of the color-focused arguments may be more effort than we wish.

This is another candidate for remove_method?