Young walnut fruits provide that same inky color to nocino, the Italian after-dinner drink made by macerating me in high-proof liquor with sugar and spices.
So I'm starting with the berries, so that I give them some time to macerate, and release all their juices, but they're gonna go on the cake at the very end, right before baking.
It was a lovely recipe that would make for great Sunday afternoon baking, but not to live on the store shelves of national retailers, because it's like soak dates overnight and then macerate the dates.