Would actually most likely be ivory. Or just plastic made to look like ivory. It would be my thoughts that Trojans would have had brass beads. And I would not think any to have a center bead. I think that yours might have been added at a later date.

Most likely the beads are ivory, not pearl. Yes, they would be an 'upgrade' but probably not done by Parker. Most any good gunsmith can fit ivory beads to a gun.