I was raised eating Huckleberries...a wild tart cousin of the blueberry.
For some reason the wild bushes have gotten scarce... So a a few years ago I was talking with a local blueberry grower, and he told me he could pick blueberries at a stage (red)..allow them to ripen for a day or two on newspapers, and they would taste very similar to the wild huckleberry I was accustomed to eating....I said fine pick me 5 gallons, he did and they tasted great..They had turned purplish, were very tart, and made excellent cobblers. Depending on the stage of ripeness when picked..blueberries will continue to....
Ripen.