Colour consistency is a sourcing problem, not a polishing one
Natural amber varies bead to bead, which is charming on a collector strand and commercially unworkable across ten thousand identical gifts. The only way to hold colour across a large run is to reserve the raw stock for that run before production starts, which means committing material early and carrying it.
For volume programmes we batch and reserve material per client and record the batch in the production file. That is what makes the second container match the first, and it is the single most common reason a bulk order disappoints when a supplier has not done it.