I'm not familiar with Japanese specifically, just general Far East, it would seem to me that it either has to be black, or it has to be braid of some kind, not just a coloured binding. I've seen some stuff finished with cord, not sure how it's attached, but I think a coloured binding would be a poor substitute. I might even try the type of binding (do you call it facing?) where the whole thing gets pulled round to the back.
Cheers Anne