Can you photograph inside the drill holes of the pearls you actually have?
This morning I'm using a magnifying glass with the enlarged setting of my screen, but it's only an iPhone4, so you know how small that is.
Last night I took out some dyed, bead-nucleated pearls to look at. It's a batch of pearls that I was trying to take the dye off of, pale aqua. Anyway, on the pearls I hadn't interfered with, the appearance of the drill holes on each pearl wasn't uniform. One entrance of the drill hole had a ring of dye concentration. The opposite entrance hole of the same pearl could look very clean, no dye concentration ring at all. A caveat with this information is that this was not a good dye run to begin with, the coverage was thin, and dye concentration spots were very pronounced.
Were they sold to you as natural-color? Were they expensive? Is the vendor well regarded here?
eh, I'm an idiot. I just remembered I have some pale,yellow-dyed pearls, so I dug them out. I was hoping to see how the light played around the dyed pearls and then compare it with the play of light in your photos, and peek into the drill holes. I'm still an idiot however, because
1) I cant see into the drill holes clearly enough to describe the layering, and
2) the best description I can come up with is that the light bends differently. It illuminates all the way around my Un-dyed pearls, and the dyed pearls don't show the same way.
so, inexperienced student vote - undyed.