They develop from pale greenish at first, then to reddish-purple and finally dark blue when ripe and mature. The fruits develop in the middle of the growing season. For more information, visit http://www.blueberry.org/faq.htm.
I don't think you understand, blueberries are purple. Get it through your thick skulls, they are PURPLE. They are called blueberries because humans are stupid! Let's recap: blueberries = Purple, and humans = stupid.