“Kabbolistically, a person should wear only white (davka)on shabbos – seems it represents chesed (while black is for gevuros).”
This is partially flawed. White and silver are associated with Chessed. Red, not black is associated with Gevurah.
Brilliant white is associated with Keter. From a different perspective, black is also associated with Keter, but it is beyond the scope of this forum to discuss that.
Blue is associated with Malchut. Shabbat is associated many times with Malchut. Each of the 6 days of creation are associated with HaGa”T NaHi”Y. Yom Rishon is Chessed (creation of Ohr), Yom Sheni is Gevura (Rakia, Mavdil — severity), Yom Shlishi is Tiferet, Revii is Netzach, Chamishi is Hod and Yom HaShishi is Yessod (creation of man, sexual balance)
“Some Rosh Yeshivas, as in CHaim Berlin etc. on shabbos would wear their talis by folding the black stripes on their shoulder UNDER the talis so that only the white part of the talis showed. This way they were yotzeh the kabbalistic need to “wear white” on shabbos.”
If that were true, then they would wear a white on white Tallis for Shabbos, and a regular black on white Tallis for weekdays. And MiDina Gemara, a person should have 2 Tallaism as noted above. However, that too would be difficult to shtimm with Kabbalas Shabbos, Maariv and Mincha on Shabbos afternoon, when Rov HaOlam do not wear Tallaism (at least not in public).