I had thought about the Ivory issue too. I still plan on pairing them together for the 2015-2016 season. I think it will still give me the best chance of seeing if there is a genetic component to this color change.
For this season (2014-2015) I'm pairing the founding male with 3 of his daughters from the 2011-2012 season, a normal, a Pastel, and a Pastel Orangebelly. I'm hoping that this line breeding will help give some insight into this puzzle.