What Color The Straps?

We all know that tefillin straps must be black - but is that necessarily true?

 The Mishna Brura says [סי' טז סקי"ט] writes that ideally they should be as black as a raven. The Biyur Halacha [same man - different font:)] adds that any black is good enough and even [dark] blue works. Rav Yisrael Gustman believed that even dark brown is good enough.

What is fascinating is that this leads to an interesting discussion of which colors make a woman a niddah. From tefillin straps directly into taharas hamishpacha....

See Sefer Halichos Yisrael [by Rabbi Yisrael Talin] page 80.