Trying to figure out claro walnut crotch vs. crotch black walnut in a single chunk of wood is going to be hard to do. I say call it what you want to call it.
Even better yet for more confusion....read this:
Some confusion exists about the nature of claro walnut because J. hindsii is commonly used as the rootstock of orchard trees. The section below the original graft is claro walnut wood, while the section above is the lighter-colored English walnut. Some woodworkers have even taken advantage of this by making the change in color of the wood a feature of their work.
Vince