I believe we had one of these sorts of topics previously, but hay I am too lazy to go and search it out so I don't mind doing this again, especially since we now have new members, and its nice to know where people's names come from.
@ironcross, its good to get that story, I'm afraid when I saw your username the first thing I thought of was the Nazi medle of the same name see Good old wikipedia, rather an unfortunate coincidence .
Actually in my case the term "dark" has nothing related to blindness. When I was a teenager I began writing a post appocalyptic story about a world where the government employed assassins to kill off anyone making technological upgrades to prevent the great war from ever restarting. The main character was a small, infinitely sarcastic knife using assassin called Dark who starts of completely loyal to the government, then when he unknowingly kills the girl he's in love with he goes on a big jaded crusade against them. Yes, it was extremely melodramatic, but give me a break I was 16 .
When I got online shortly after, I had this idea that you should never use your rl name on the internet (remember this was the early two thousands), so I chose the name Dark, which also has an interesting relation to my rl name. Since in Rl my first name is Luke, which means light.
When "dark" is taken on a game or other system, I use dark empathy, or dark tenor, indeed those who were here before 2006 will remember that I originally registered as dark empathy, then got my name changed to just dark instead.
these days I actually answer to Dark just as readily as Luke, and like the crew in the matrix, consider it to be pretty much my use name, indeed my lady first new me as "dark" since we ran into each other on a mailing list.
With our dreaming and singing, Ceaseless and sorrowless we! The glory about us clinging Of the glorious futures we see,
Our souls with high music ringing; O men! It must ever be
That we dwell in our dreaming and singing, A little apart from ye. (Arthur O'Shaughnessy 1873.)