Diversity meant more than the colour of your skin, your sex or the god you believed in.  Diversity was in your customs and culture, it was the people you loved, the things you enjoyed, and any and all forms of self-expression.  It had been a difficult road to rid humanity of these 'dividing influences', but the decimation of the Last War left just enough survivors to be moulded into a homogenous society.
Untold time had passed since the War, but it's horrors rested equally in the minds of all, as did the divisions within humanity that were believed to have caused it.  As a whole, the species was declared irredeemable- any form of difference within society would lead to conflict, and in turn, the terrible destruction that had nearly ended their world.

Today, a person stands in front of their wardrobe.  It does not matter what they look like, because they all look the same.  There are several shirts hung, but there is no choice to make.  It is a work day, so they wear gray.  The red shirt is for the Day of Remembrance only, and the white shirt is for the Winter Holiday.  It is unthinkable to wear these outside of their given purpose. 
Sin is a word long erased from the collective consciousness, but the act carries a similar connotation.

Outside, another person (or it may be the same one, there is no way of knowing) walks within a sea of gray.  Identical faces, identical clothes- save for a few stains.  Their shirt is beginning to lose its colour, almost to the point where it will need to be replaced, else it risks being a distinction between them and others. 
Vocation is one of the few areas where they possess a slight amount of choice, and the uniform mass of people splits and reforms throughout the city as they make their way to their respective workplaces.  Identical figures with the same bored expressions sit on public transport, lives devoid of entertainment in the form of books or art or music.  There is nothing but what is, there is no us and them, there is only we.

The same polite smiles are exchanged between coworkers without names, meaningless small talk that rarely goes any further.  When no one is an individual, relationships become obsolete.  It is a lonely existence, made up of people who have no word for loneliness, and no ability to name the feeling that chokes their mirrored hearts.  They want something, but they do not know what that something is. 

Perhaps somewhere, people are different.  Perhaps there are leaders, of a sort, unnamed and unknown, behind the masses, who designed this society and allow it to run.  Or perhaps they are long gone, and this autonomous, empty world runs, self-sustaining, of its own volition.  No one left to know the world that was before, the diversity among humans and the beauty of it.  Independence, pride, creation.  Connection.
There is no way of knowing.