A waxy covering coats some blue-colored fruits — such as blueberries, dark grapes and certain plums. This wax contains a host of tiny structures, each less than a thousandth the thickness of a piece of paper. Such nanostructures scatter blue and ultraviolet (UV) light. To our eyes, that makes these fruits look blue. Birds — which can see UV light — probably see such delicious snacks as bluey-UV.
But if you rub off the outer layer of wax, a blueberry no longer looks blue — or red. Instead, it’s completely dark, Rox Middleton says. Middleton is a physicist who works at the University of Bristol in England and at Dresden University of Technology in Germany. Structures in the fruits’ waxy outer layers create blue hues that are faux, her team now shows.
I thought so too, until I saw the truth.
https://www.snexplores.org/article/why-blueberries-blue-crystal-pigment
Sadly, when you blend blueberries in a smoothie it turns your smoothie purple.
Fun fact in French their names have nothing to do with blue