Why do men wear black hats?

Why do men wear black hats? What does is symbolize and what is the purpose behind it?

Rabbi Avigdor Miller zt"l was once asked, "Must all religious people dress like they are in mourning? Why should they all dress in black?"

He answered: "Black is not a sign of mourning, black is a sign of nobility. They dress like an important person... It's a sign of importance. And so when Jews wear a black hat, it's a sign that they are "Mamleches Kohanim", it's a nation of important dignified people. And that reminds them that their behavior should be dignified. Now it doesn't mean that if you wear a white straw hat, that you are permitted to be undignified. Nevertheless, when people choose dignity in their garments, it has a very big effect, an unfailing effect on their character...

[W]hen you dress in a dignified way, you become dignified. And that's why it's always important for men and women to remember, dignity in clothing...

We have to learn how important it is to be dignified in dress. That's what Hakadosh Baruch Hu wants at all times. And that's going to change a man's inner behavior, his mind is attuned to his externality".

Source:

http://gemsoftorah.blogspot.co.il/2010/05/fw-moment-with-rabbi-avigdor-miller-zl.html

Hats were once a form of dress that signified self respect. Just like the Queen would never leave her house in jeans, so too men, from the fifties and before, always wore hats. The world started dressing more casual and it truly reflects their actual lack of self respect in general. But Jews know that how you dress affects the way you view yourself. I.E. If you wear your hair long, chances are you don't have a white collar job. So we don't compromise on our appearance, and that includes hats. It's a matter of self respect. If you see someone wearing a white hat but it's dirty and smashed, that might mean he doesn't really know himself why he is wearing one. Sometimes we just get used to a certain way of doing things and we forget to ask why. Kudos to you for asking.