As in the case of walnut levain, a reaction occurs between the tannins in the skin of the walnuts and the sourdough whole
wheat dough around it which causes the crumb to turn noticeably purple.
Not exact matches
I can see this being very hard to do without the gluten in
wheat flour... you might try using your hands to mold the
dough around the apple rather than rolling it out and trying to wrap it that way.
I've messed
around with 100 % whole
wheat dough, and I wouldn't really call it pizza.