I have no idea, in the article I read it sounded like they did something to make the apples turn black. Like dying them perhaps. Everything about these Black Diamond apples seems extremely fishy to me. The first article I read made it seem as though light and temperature made them turn purple. In the second article I read, it seemed as though they picked the darkest looking apples already, then infused them with something that made them turn darker.
There are dark skinned apples out there that CAN look almost black. Black Diamond probably tastes terrible and if you are looking for a dark skinned apple, you should turn your attention towards Black Oxford instead.
A Red Delicious Apple
https://pbs.twimg.com/media/DTqtWB6U0AEgpXf.jpg:large
Here is a sport of Red Delicious called Star King that is darker than those in America.
https://dreamscomtrue.net/StarKing.html
Here is a dark apple they call Nagano but I believe that is where it is grown, not it’s name.
http://vegemart.net/apple/kind/03_ab.html

Australia presented the Bravo – Apple with black skin
https://siriusap.com/en/news/27-avstralija-predstavila-bravo-jabloko-s-chernoi-kozhicei.html
https://www.theblacktruffle.com.au/story/comparing-apples-to-apples-2/
