Black Socks

When I'm doing the laundry and come across an unpaired sock, I put it on the little shelf above the dryer until its match turns up later. Over the four years we've lived here, though, a few unmatched socks have accumulated up there with their mates apparently permanently lost. There are nine of them, and they are all black.

The only possible explanation I can think of is that we have some sort of dryer gremlin with a black sock fetish. How else could we end up with nine distinct unmatched black socks, and no unmatched socks of any other color?