Posted on: 2021-02-14 10:29:31 UTC
There would be multiple ways to do it. Off the top of my head, one could add a bit of activated charcoal powder, squid ink (works with pasta!), or plain old food coloring to the dough. There are probably other options, too--heck, black rice exists. Assuming anyone might make flour out of it, you could use that. I don't know what was used in what you linked, though--even if I could read it, or had a minute to feed it through a translator, it doesn't look like there's a recipe in the text. Could be wrong, though!