Well it could have come from the Recessive White hen, right? Without receiving two copies of the white gene, one from mom and one from dad, it's probable that the chick would display whatever her double dose of white is covering?
You sound like me with the roosters. lol I've got the three adult SLO with three laying SLO hens and one almost point-of-lay SLO pullet. Plus out of the 17 Lavenders I'm growing out I'm pretty sure there's five males. And with the BBS Orps I'm looking to get I want three blues and two splash hens, and one black rooster and one blue. I'm going to be up to my eyeballs in roosters.