Elderling Creations Theory (Spoilers through all the books and Dragon Haven)

[Mervi]

It's in very beginning (2nd paragraph) of chapter nine of AA, "Fat Suffices". Fitz is describing the very few know facts about the Fool and says

The Fool was almost certainly born of human race, though not entirely of human parentage. Stories that he was born of the Other Folk are almost certainly false, for his fingers and toes are completely free of webbing and he has never shown the slightest fear of cats. The unusual physical characteristics of the Fool (lack of colouring, for instance) seem to be traits of his other parentage, rather than an individual aberration, though in this I well may be mistaken.