Just as its name implies, black cocoa powder is black...not just the usual dark brown of cocoa powder, but a bold, saturated black color. It's ultra-alkalized so it has a deep, dark color and an intense chocolate flavor. This is the cocoa you want if you're looking to make Oreo-esque cookies or black chocolate cakes! Also, try mixing some of this cocoa powder with hot water to make a paste, then adding it to buttercream--you'll get a dark black frost;ing with an intense chocolate flavor.
Black cocoa powder pro tip: I do find that it's more drying than other cocoa powders when I add it to baked goods, so I usually use a combination of regular and black cocoa powder when I'm baking. Try substituting 1/3 of your regular cocoa powder with black cocoa, and see how you like the results!