Blueberries are purple except when they are green. Then they are red.
Blueberries have no responsibility to be the color of their name. The name is arbitrary. In fact blueberries are indigo, same as aubergines, "blue" jeans, indian corn, the sixth color of the rainbow, and a few other natural effects.
The rainbow is another example of arbitrary names. Isaac Newton, the gravity guy, decreed that the rainbow should be divided into seven colors because there are seven days in a week. Go figure. Modern students did not like the color indigo being invisible to human eyes so they arbitrarily assigned new names to eliminate it from the rainbow.