People tend to think the dark, black color is from added squid ink. It actually is from cocoa powder and chocolate chips.
I bake French bread every week. I wanted to make one with a different flavor for once.
Hint 1 - If you want to make it pitch black, use black cocoa powder. Hint 2 - The dough itself is pretty bitter, so it tastes better with a generous amount of chocolate chips.
Enjoy Japanese food around the world.