Must the Shel Rosh straps that dangle in front of one’s chest have their black side face up?
The Poskim rule that the straps are not to be turned over [onto their white side], neither by the Tefillin Shel Yad nor by the Tefillin Shel Rosh [and are hence to have their black side face up]. However, this only applies by specific areas of the straps. It is only necessary to be careful that the straps do not turn over [from their black side to their white side] by the straps of the Shel Rosh that surround the head [and are used to fasten the Bayis to it] and by the strap of the Shel Yad that surrounds the bicep a single time. However, whatever is bound afterwards [onto the bicep and arm], and likewise whatever dangles in front of him from the strap of the Tefillin Shel Rosh, there is no need to be particular about it at all that it does not turn over being that [these parts of the straps] are not from the main part of the Mitzvah [of Tefillin]. [Thus, from the letter of the law, there is no need for the straps that dangle from the Shel Rosh and rest on one’s chest to have their black side face outwards, and it remains perfectly valid if their white side face outwards. Nonetheless, it is proper due to the beauty/Noiy of the Mitzvah, to make sure that even these straps have their black side facing up, and to turn them back over if necessary.]
It is not necessary for the strap that dangles by the chest to remain with their black side up. Nonetheless, it is proper due to the beauty of the Mitzvah, to make sure that all the straps have their black side facing up, and to turn them back over if necessary.
If one sees that someone’s Shel Rosh straps turned over, is one to mention it to him?
As stated above, there is no requirement for the straps that dangle in front of the chest to have their black side face up and hence certainly there is no need to mention this to somebody. The only time that mention needs to be made is if the straps by the head, or the first strap that wraps around the bicep, is turned over. Nonetheless, it is a widespread custom of the world to make sure that even the straps that dangle in front of the chest have their black side facing up and to make mention of this if one sees another person strap’s turned over. This is done due to Noiy Mitzvah, as explained above.
If the straps of one’s Tefillin are black on both sides must he nevertheless be careful that the strap does not turn over?
Yes, he is to beware even in such a case that the strap does not turn over, and that the black shiny side is facing up.
 Admur 27:19; M”A 27:17 in implication of Tur and Michaber ibid; Tur 27, as brought and explained in Machatzis Hashekel ibid; Yad Aaron on Tur; Elya Raba 27:13; Shalmei Tzibur p. 37; Shesilei Zeisim 27:28; M”B 27:38; Kaf Hachaim 27:50; See Michaber 27:11; Piskeiy Teshuvos 27:20
 P”M 27 A”A 17; M”B 27:50; Kaf Hachaim 27:50; See Machatzis Hashekel ibid “By the 7 straps of the arm one does not need to be so particular”
 Siddur Beis Oved Seder Hanachas Tefillin 16; Kaf Hachaim 27:51; Piskeiy Teshuvos ibid footnote 181