Monozygotic twins have all the same genes, but they aren't ever EXACTLY alike, just very similar. The same kinds of genes can get expressed in different ways. They can both have the same gene, but it may be "ON" in one twin and "OFF" in the other, which will result in slight or even extreme differences in appearance. I had twins for roommates and I could always tell them apart, one was taller and had a thinner face. At a distance it was hard to tell, but close up it was pretty obvious who was who. Some twins look more alike than they do, but there are always going to be differences.
I'd bet you could get low, 50% and high white pieds from a clone of the same animal.