The Shulchan Aruch includes a disagreement between the Mechaber (R Yosef Karo) and the (Ashkenazi) Ramo. The Mechaber’s view is that the strings should be the same colour as the four cornered garment they are attached to. In that vein someone wearing a Kapote which is black and has four square edges, would need to wear black Tzitzis. That’s my understanding of the Mechaber. The Ramo states that Minhag Ashkenazim is different. Ashkenazim don’t look at the colour of the garment as determinant, rather they always wear white. Undoubtedly this is not a Minhag from the time immemorial. Rather, when the Jews had preserved the tradition of Tcheles from generation to generation it is reasonable to conclude that the strings were not all white. Indeed, we see even amongst Sefardim like the Rambam, and others such as the Ra’avad and Tosfos different ways to utilise and incorporate the Techeles string.
The tradition of Identifying/finding Techeles was lost. There is the famous Radziner Rebbe who thought he identified Tcheles, and the subsequent debunking of the Radziner Techeles by Chief Rabbi Herzog and others. About 15 years ago the murex trunculus (as I recall, I could be mistaken with the exact name) enjoyed very strong halachic and scientific support as being authentic T’cheles.
Rav Soloveitchik opposed attempts to identify and conclude what T’cheles was as he was very much the Masoretic Jew from Beis HoRav (stretching to the Vilna Gaon). As such, where a mesora/tradition was lost, that was the end of the story, and one would need a Novi/Melech HaMoshiach to confirm the source of the T’cheles blue.
According to Kaballah, the Sefer Hachasidim related that he saw in a prophetic image that God wore white Tzitzis on a completely white garment.
The Mishna Brura opines that it is best to wear a pure white garment and white Tzitzis, as in this way one fulfills both the opinion of the Ramoh and the Mechaber.
It is rumoured that the last Lubavitcher Rebbe’s father, Reb Levi Yitzchok הי׳ד who was an accomplished Kabbalist, wore a plain white Tallis and white Tzitzis.
Mori V’Rabbi Rav Hershel Schachter argues that today, based on the Gemora in Menachos 40a, that the Gemora states explicitly that someone who wears Indigo coloured strings as a substitute for Techeles is fulfilling the Torah command of Tzitzis. Therefore since in our day we have something which can be called ספק תכלת, possibly Techeles, there is a cogent argument to no longer follow the Ramoh’s custom, and to wear modern T’cheles, since it’s a ספק דאורייתא, a Torah doubt, for which we normally are careful to be concerned about.
Clearly, Rav Schachter, arguably the most accomplished of the Rav’s Talmidim, doesn’t agree with his Rebbe, Rav Soloveitchik (during which time this T’cheles wasn’t yet (re)discovered.
Rav Schachter opines that Rav Elyashiv’s view that one should continue wearing white, must be based on a reason that Rav Schachter didn’t merit to understand. I seem to recall Rav Schachter meeting with Rav Elyashiv and this was one of their conversations.
I have a set of the first T’cheles of the new type that have been sitting in my cupboard for many years. I haven’t looked into the matter since I read Rav Soloveitchik’s view.
I’m interested in any views which may differ from the rather compelling logic and psak of Rav Schacter. I know that Chassidim (and today’s Litvaks are no different) look to their Master and follow their Rebbe/Daas Torah behaviour and practices.
I’m interested in halachic arguments against Rav Schachter’s logic.