And as for why sheep have red spots: Stephen Smith points out that sheep are sometimes marked with red dye, and he is right, of course....but why are nearly ALL Staffordshire sheep red? Nick Burton told me a long time ago that spots are red "because they look pretty that way, of course" and Nick is seldom, if ever, wrong on the aesthetics of pottery. I have seen black sheep. I have on file a black and white sheep, and a pair of black sheep, all reclining....and a friend has just sent me a picture of a solid black sheep standing in front of a spill holder (it looks very Walton-like).
Andrew Dando sent me this link to a modern-day farmer with orange sheep. Enjoy the story! And thanks to all for the input.