[Avodah] Tefillin retzuos black on both sides?

[David Riceman]

Marty Bluke wrote:
> My son's bar mitzva is approaching so I had to order tefillin for him.
> In the process I heard of a new chumra, the retzuos should be black on
> both sides. Does anyone have a source for this? Is this really a new
> chumra or is this an established minhag? I personally never heard or
> saw retzuos like that until now.
>
>   
See H. Tefillin 3:14, though I've never encountered this in practice.

Incidentally, I had hoped to finish researching the tefillin on Hol 
HaMoed posts over Shabbas, but I got distracted.  Soon, DV.

David Riceman