OK, so Christmas pearl isn't a technical term, but this is a very unusual Tahitian pearl - usually, fancy overtones occur in circular, radial patterns. This pearl has its overtones almost split down the middle. With a very slight shift in angle, the pearl looks reddish cherry, and the other is a vibrant green. A color shifting pearl! If a watermelon tourmaline exists in pearl form, this is it. 
 
It's drilled on the bottom to show this effect, so should be set in a pendant/other piece that allows it to face forward. (Andrew's note: This might be the most incredible brooch pearl, if you're into that)