Because Pat's black! No, not his skin. He's an anthropomorphic cat, standing at about one and a third metres tall, whose fur is a glossy black, with a blotch of white at his tummy. His eyes are blue, like eyes, and look like they can see your very soul...
Pat got his start from a set of stories (which are not online) and as such, is immortal, quite versed in the mysteries of nanotechnology, and can speak many languages.
His name has no relation to Pat Califia, Pat Buchanan, Pat from the "It's Pat" sketches on Saturday Night Live, or Pat The Fuzzy Bunny.
You might see him on the few MUCKs he frequents, such as Tapestries and Realms, especially the former. Be aware if you visit him on Tapestries that you must be an adult; mature (and sometimes immature) things happen there.
(By the way, the sentence in the title and the header refers to an event on the Internet during the beginning of 1996, during which which many people turned their pages black for 48 hours, in dispute over the CDA, the Can't Do Anything, er, Computer Decency Act. Some people still have their pages black, even though the law has since been overturned as unconstitutional. Check out The EFF home page for more information.