The Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909), in Parashat Lech-Lecha (18), writes that one must designate clothes especially for Shabbat (listen to audio recording for precise citation). The prophet Yeshayahu (58:13) declares that one must give honor to Shabbat ("Ve’chibadeto"), and the Sages explained that this is achieved, in part, by wearing clothing on Shabbat that one does not wear during the week. The Ben Ish Hai adds that although many people are not careful to designate a particular shirt and pair of pants for wearing on Shabbat, those who do have a special shirt and pair of pants for Shabbat are deserving of blessing. Indeed, the Ben Ish Hai notes, this was the practice of the Arizal (Rav Yishak Luria of Safed, 1534-1572), who had special "Kavanot" (intentions) while putting on his special Shabbat clothes that have the capacity to bring Kedusha (sanctity) upon a person.
The Ben Ish Hai also writes that according to the teachings of Kabbala, one should not wear black clothing on Shabbat, and should try to wear white clothing. Hacham Ovadia Yosef, however, notes that nowadays, when it is not customary to wear white suits on Shabbat, wearing a white suit on Shabbat would be an expression of arrogance. Furthermore, Hacham Ovadia observes that it has become customary for Torah scholars in many circles to wear black suits on Shabbat, and therefore this is certainly permissible. In fact, the Gemara in Masechet Shabbat (147) explicitly states that the Torah scholars in the Babylonian community of Pumbedita wore black clothing on Shabbat. Nevertheless, Hacham Ovadia writes, there are some who endeavor to wear gray or blue suits on Shabbat, in deference to the Kabbalistic tradition to avoid wearing black. Hacham Ovadia adds that one who wishes to observe the tradition to wear white on Shabbat may wear white garments in the privacy of his home, or wear white undergarments that are not visible, so as not to appear arrogant.
The Ben Ish Hai rules that strictly speaking, one is not required to designate a pair of shoes especially for Shabbat, though those who do so are deserving of blessing.
Summary: One should designate a set of clothing – a shirt, pair of pants, and suit – exclusively for wearing on Shabbat. Some have the practice to avoid wearing black clothing on Shabbat. Strictly speaking, one is not required to designate a pair of shoes for Shabbat, though it is commendable to do so.
