Sadly, I think Nintendo would dispute the idea that those characters are "black" in the way we define it.I was surprised in the first place Nintendo chose to make black/brown characters as the faces of Splatoon 2 (default inkling girl, default octoling girl, Marina) which is their biggest IP in Japan right now.
The unfortunate truth is that when a Japanese-designed character is meant to be black, they usually look pretty stereotypical, so there's zero ambiguity. Otherwise, the character is "ambiguously brown." They could be African, Indian, a Pacific Islander, or just a Japanese person with a deep tan. Most often, it's the latter.
That's part of why stuff like this really stings. It makes you realize that you were giving a company credit for a progressive assumption (or "headcanon") that we all collectively agreed upon.