AU: Scientists now know why this orange turned purple out of the blue
ABC News: Scientists finally know why an orange purchased from a fruit and veg shop in suburban Brisbane turned purple, hours after it was cut open. The answer? Naturally occurring anthocyanins in the orange reacted with the iron particles found on the recently sharpened knife which was used to cut it, causing it to go purple. "These pigments are not known to represent any risk to human health."