a suit is suit. lets get real. a white shirt is a white shirt. two button or three button jackets or white on white shirts. its basically the same thing. your argument on that is really not withstanding. we dont all have to buy the same brand white shirt or suit, so each one will be slightly different from the next one. and if the uniform meant nothing then why do our Gedolim wear it every day! Gedolim do everything they do for a reason. they are not walking arond in a blue pressed shirt. or brown dress shoes. or jeans on a casual day. they wear dark pants, white shirts, hats and jackets.
If a suit is a suit, then why can you spot a fashionable guy (wearing a dark suit and white shirt) easily from someone who is wearing an “out of fashion” suit? Its generally easy enough to see and I know VERY little about mens suits.
I know plenty of people who wear white shirts and dark suits day in and day out – and arent Jewish. They generally have higher pressure jobs (Wall Street and such) and that is what they are used to wearing.
As to why gedolim do it – why don’t you ask them? Maybe its because it makes it easy to get dressed in the morning. They don’t have to think about “which shirt matches what suit”? Maybe they do it because it makes laundry easier on their wives? Or maybe its because its easy to find dark suits and white shirts? GO ASK THEM AND DON’T ASSUME.
Also, realize this is a relatively new phenomena. Our parents generation (OK, I don’t quite know how old you are) did not only wear dark suits and white shirts. Even the most frum ones.