The Gra has a famous comment about Shabbos Chazon. The Rama based on the Rishonim paskens that a person should not change their clothes for Shabbos Chazon, but rather wear weekday clothes. The Gra disagrees and says that אבילות בפרהסיה is assur and wearing week day clothes is אבילות בפרהסיה. The minhag nowadays seems to be like the Gra.
Recently, I heard that a number of Charedi rabbanim are going back to the psak of Rama for the following reason. Anyone who knows the (non-Chassidish) Charedi world, knows that there is very little difference between weekday clothes and Shabbos clothes, especially for Rabbanim, Roshei Yeshiva, etc. They wear a dark suit and a hat all the time. When I see the Rabbanim in my neighborhood I can never tell the difference between weekday clothes and shabbos, many of them wear a long black frock 7 days a week, and those who don't wear dark suits. Therefore, for them, it is not אבילות בפרהסיה to wear weekday clothes, very few people if anyone will be able to tell the difference.
The same sevara applies to the more modern world in America where many people wear suits all week to work and a similar type suit on Shabbos. Again, very few people would notice if they wore a weekday suit on Shabbos and therefore it would not be אבילות בפרהסיה.
This sevara is brought down by the Aruch Hashulchan where he uses it to explain how the minhag changed.
