For nearly a decade, scientists have been hunting for the gravitational wave background, a faint but persistent echo of gravitational waves thought to have been set off by events that took place ...

Supermassive black hum: Scientists discover gravitational wave background that permeates universe The source could be merging black holes — or something more 'mind-bending' ...

They work by vaporizing an amount of solid ink and letting that condense on the paper, so they may leave black halos around print as well. Also, they're pretty rare.

I didn't see black as an option in the background color list. I'll check again when I get home from work. <BR><BR>Yes, rtfm indeed. I actually read it, believe it or not.