My Rosh Hayeshiva ZT”L used to talk about how he came home one day with a black suit. His father, a talmid of the Alter of Slabodka, made him return it. He knew that wearing black and white, in imitation of chasidim, was a poor substitute for actual internal development.
As for why Bigdei Shabbos are different than Bigdei chol, this is a bayasa bekuscha. Shabbos is not weekday.