The secret of blueberries revealed - Nature. Blueberries appear blue because in the very thin layer of natural wax that covers them there are crystalline microstructures that reflect blue light and ultraviolet rays.
This was discovered by British researchers at the University of Bristol, thanks to a study that paves the way for the development of new sustainable, biocompatible and even edible dyes. The ultra-thin dye is approximately two thousandths of a millimeter thick, appears blue and reflects UV rays well.