Unusual Bird: Northern Cardinal with unusual plumage

I have been watching this cardinal since he got his adult plumage. He is now in his fourth spring! I thought surely as a fledgling he would lose that one white-looking feather when he became an adult. But the odd feather stayed! He is easy to pick out from the other cardinals – the feather appears white from a distance. He has a mate, I have seen him feeding his mate over the past two seasons. I have been watching for more fledglings with similar plumage, but have not seen any so far. I am not sure that leucistic is the correct term, but you can let me know!