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I honestly can't call to memory which is which. If you look up walnut on wikipedia they list defining characteristics of each species, and their sub-species. Also lists the regions they USUALLY grow in. That part is pretty much a "guess-timate" because according to that chart heartnut walnut trees shouldn't be any where near me, yet my woods are littered with heartnuts.
If you buy (or bought) it from a store they can sometimes tell you. But if it's an "all in a box" hardware store, you may be S.O.L. Wish I could tell ya what any of it looks like sesaoned, but I can't. I lost a lot of my trees to cursed carpentar ants, as in 15-20, and I just bought this place in April

Yup, its black walnut, phew...

Black walnut is just the species name, mostly 'cause the outside of the nut is black once the green smelly goo wears off.

The wood ranges from dark brown in the heartwood to nearly white in the sapwood. It's never actually black.