Even with "black sheep" with green eyes, it would not explain two people with genetically blue eyes having children with eyes that are a color other than blue. I know people with "vivid blue eyes" that, when the light hits them in a certain way, they look a bit greenish, and I assume that they are not the result of two recessive genes. I'm no geneticist, but I would guess that pale blue eyes are not true double-recessive blue eyes and thus could result in a brown-eyed gene being passed down.
BTW, people whose eyes are neither true blue nor true brown---be they green or pale blue or hazel or gray or caramel---most likely have one blue-eyed gene and one brown-eyed gene and have a very, very common "mutation" that produces not brown eyes (as one would expect with one brown and one blue gene) but another color.