Here are three pearls I bought my wife while in Disney. All three were bought at DTD.
The first (black) on was the most recent pearl. We had bought roughly 10-12 pearls from the Pearl Factory stores and never gotten a black one. As we were telling the CM,

, out popped the black one. My wife was so excited.
The middle pearl has a green tint to it, thus why it was mounted with emeralds. The picture does it no justice, the emeralds really bring out the green color. BTW, the ring was purchased from a jeweler back home not at WDW.
The third one was just a plain old white pearl, nothing special about it.
My wife has a gold pearl (her first pearl, from Las Vegas though not WDW) that literally looks as if it was dipped in gold. I'll see if I can get a picture of it later.
On an aside, a CM at DTD told my wife and I that every color you see inside the shell was once the color of the pearl. I don't know anything about oysters other than they make pearls and taste good on crackers with hot sauce, so I can not affirm or rebut that statement. Just know early in this thread there was some discussion about certain oyster that only produce black pearls. If that's the case, I'll be looking for that particular oyster on our August 2010 trip.
Jerry