You wrote in the Background notes to Ta'anis 22:
12) [line 12] SAYIM MESANEI UCHMEI - (a) who was wearing black shoes , like the practice of the Nochrim (RASHI); (b) who was wearing black shoes and shoelaces , like the practice of the Nochrim. Benei Yisrael wore black shoes and white shoelaces at the time (TOSFOS to Bava Kama 59b DH Havah and to Sanhedrin 74b DH Afilu, citing RABEINU TAM)
WHY did he do this? what does it signify?
Question from L.A.
It signifies that even though they were not traveling to Yerushalayim for the festival (traveling being referred to as "shoes," as the Gemara in Chagigah 3a teaches from the verse, "Mah Yafu Pa'amecha ba'Ne'alim (shoes) Bas Nediv"), nevertheless they grieved (signified by the color black), from their homes, over the destruction of the Beis ha'Mikdash. As a result of their devotion to the Beis ha'Mikdash and their grieving over its loss, there was one "benefit," and that was that wherever they were exiled to, the Shechinah went with them (signified by the white among the black).
M. Kornfeld
MK:ys