Just to make one correction to your opening statement.
WHITE GOWNS ARE A TAKONAS CHAZAL.
It comes from the fact that in the times of Chazal the concept of colored clothing was a huge expense as it requires much much much work when you are threading the loom. When making a pattern, every few lines the thread needs to be changed for the design to be nice and pleasant on the eye. Hence the great jealousy the Shevatim had to Yosef when Yaakov made for him a kesones pasim (a striped suit). It wasn’t as simple as Yaakov walking into Macy’s and buying 10 straight black suits and Yosef got a pinstripe. The work of making a striped suit was a tremendous amount of work.
Chazal knew that not every kallah would be able to afford a fancy gown and therefore were מתקן that every kallah wears white כדי שלא לבייש את מי שאין לה.
(Similarly, on Tu B’Av all the marriageable aged girls borrowed WHITE dresses for the same reason).
Heard once from Rav Nissin Kaplan Shlit”a that what is referred to in the zemiros of Friday night. One of the descriptions of Shabbos is that she is ככלה בין רעותיה משובצה. Every kallah wears white. So how do you know who is a fancy kallah and who is a simple kallah? By her friends. If her friends are all dressed to the nines, then you know she is fancy kallah. And if her friends are dressed shabby, its probably a more simple kallah.
So too when it comes to our Shabbos. If you really respect Shabbos, for the sake of Shabbos, you will make sure that there is a beautiful Shabbos in EVERYONE else’s house. Because if the fancy flowers/clothing/food is truly for the sake of Shabbos, what difference does it make if its on your table or the table of someone else??? And how more special would it be for someone who can’t afford it!!
That is connection we are referring to of Shabbos and the Kallah. Just as the Kallah’s friends tell us the where she stands in society, so too, the way we care for our friends Shabbos tells us how much we respect the Shabbos!