After making several blue-berry pound cakes for gifts, I found tht even when the berries were gingerly and delicately folded into the batter, their purple juices left streaks in the batter, leaving the baked cake slightly blue-gray on the inside.
I finally wised up and added the blueberries in a different way: I plopped spoonfuls of plain buatter into the cake pan, sprinkled a few blueberries on top, and then continued layering the batter with the blueberries until the cakes were finished. The result was a well-distributed berries and a prettier yellow cake. The only trick is to be sure that you save enough spoonfulls of the batter to cover the top layer of berries; otherwise they'll burn during baking.
