All Black

At the end of this week’s parsha we are instructed about the mitzvah of tefillin. The Talmud (Menachos 35a) teaches us that Moshe was taught that the retzuos (straps) of tefillin must be black. This would seem to mean that the entire top side of the reztuah must be black. The other side can be any colour (not red). Traditionally, this was indeed the appearance of retzuos – black only on the top. However, recently some people have reztuos which are black on both sides. What is the reason for this?

If a retzuah has even the smallest area which is no longer (or never was) black, its kashrus is questionable. To avoid this problem, the following idea was conceived: soaking the retzuah in black paint so as to saturate the entire retzuah. This eliminates doubts regarding white spots on the retzuah because even if a bit of paint fades or scrapes off the surface, the visible part remains black.

Some authorities encourage this whilst others hold that it is not necessary.
(Inside םת”ם – A Complete Buyer’s Guide by Rabbi Reuvain Mendlowitz)