Pour through a strainer to remove skins. To strained blueberries add buttermilk and plain yogurt, stirring to mix well. Refrigerate until thoroughly chilled.
Place raspberries in a strainer.
With the back of a spoon, press berries to remove juice and pulp. Refrigerate until thoroughly chilled. To serve the soup, divide the blueberry mixture among two bowls. Divide the raspberry mixture in half and carefully add to one side of the blueberry mixture in each bowl. With the tip of a knife, swirl the blueberry and raspberry together.