Visually they are nearly impossible to tell. They may or may not have any white on them at all. Some will have a white dot on the top of the head, that is a very good indicator. They can have a white throat patch like this girl in the photo. They could also have white secondaries that you...
Your hen is split White, the young bird in the last pic is a cock.
A Dark Pied is a bird that carries two Pied genes, and a split White carries one White gene. Neither is a color, they are both patterns.
Every bird carries two chromosomes getting one from each parent and when they breed...