He looks Porcelain (color). I'd question if he's Leucistic, as he looks like he should if he's pure, just wrong color. As far as mutations like this, @NatJ might be more helpful.
Ok.
I'm questioning if your hen is Leucistic or Albino. I'll look more at the pictures when you post them though. Unless there's a recessive gene, it could be one of those mutants instead.
Can you get pictures of her full body, legs, face and comb please? Did the farm have any other breeds/colors of chickens where this hen is a possible mistake?