Speaking of "pigs", here's an excerpt from "Folklore, Volume 16 By Folklore Society (Great Britain)" that relates to the subject of demons being described as being the color black:

Chapter: Folklore of the Wye Valley, page 175
"Ghosts we had a plenty, and of the most commonplace kind, the ordinary road or lane ghost, taking the form of a black sheep or pig (I may mention that our pigs are usually a beautiful pink)."

From
http://books.google.com/books?id=YEcKAAAAIAAJ&pg=PA61&lpg=PA61&dq=devil+black+in+folklore&source=bl&ots=TS32Qlf01o&sig=SbD0BamE2