Thank you Dave for your insights. As soon as you interpret the images, I can see what you mean.
The goldy ones were what I thought were the stray cultureds...not to be disdainful of them, but although they look the most beautifully gleaming and pretty in the box, somehow I'm always drawn to the wrinklier, more textured, more 'interesting' pearls (I think this must offer some insight into my personality, haha!)
The dark patch on the disc shaped pearl is a cavity which I cannot seem to clean...I can (using my interdental brush!) feel round the edges of this cavity through the drill hole. The grey pearl also has dirty cavity all the way around. Maybe I'll try taking the pics in the dark next time.