It's just a Pastel, but it's one that the breeder had chosen to hold back to raise up as a future breeder. For whatever reason (funds, cage space, etc) they've decided to sell it. By stating that it's a holdback of theirs, it implies that it's one of the best looking ones that they produced. Nothing is differently genetically about it, although it may have a higher price tag due to its looks and/or size.