Modern day Temani Rav answers questions about tefillin: 1) Regarding the color black of the tefillin straps:   Answer: The black color of the tefillin straps are Halachah LeMoshe MiSinai one needs to be stringent with their blackness. Even when the straps are longer than the minimal Shiur (length) needed, one needs to be careful about the blackness of the straps (so that they shouldn't lose their color or have non-black spots). The back of the strap should be the color of the tefillin (box) for beauty, this aspect does not prevent one from fulfilling the Mitzvah nor is it accepted custom. The tefillin (box) are black for beauty and color does not hinder the Mitzvah.     2) Regarding the placing tefillin:   Answer: The amount of wrappings on the hand does not make a difference however there must be a complete knot (tie) meaning that the straps must be wound all the way from where the tefillin sit all the way to the finger. One may not place the tefillin of the head until the tefillin of the arm has been tied completely. It is enough if the strap is placed on the finger. The amount of windings is not mentioned in the Rambam. The important thing is that the strap be wrapped from where the tefillin are connected at the upper arm to the finger and be tied.