Twisted asked “A bigger kasha is where did the white dress come from?”
It is actually a takana that chazal made “ksei shloi l’vayeish es mi sheain la” In order not to embarrass someone who doesn’t have.
In the times of chazal most clothing were white, because colors meant that you had to dye the threads early on in the process of making the clothing. This was a major and expensive job and many did not have the means to do so.
When you realize this, you can understand why the ksones pasim that Yaakov gave to Yosef was a big deal. It wasn’t that the brothers got solid black (or white) and Yosef’s was just striped, the whole jacket was made from scratch specifically for Yosef at a great expense, thus showing the world that Yosef had special status in the eyes of his father.
I once heard from Rav Nissin Kaplan (from the Mir) that the pshat is zmiros l’shabbos, Kol Mikadesh, “K’Challah bais reoseha Mishbatza” (like a kalla who is beufified by her friends) is refering to this thought. That every kalla looks the same, because of this takana of chazal, but if you wantto know which kalla is fancier or more wealthy, look at her friends, if they are wearing colors than this is a high class wedding, but if they are wearing white then the kalla is from a more basic home.
So to with Shabbos. By the way one makes sure his friends and neighbors have a beutiful Shabbos is a reflection of his own respect for Shabbos.
(Sorry for such a long answer to a short question).