The Black Diamond is a rare apple breed that has a sweeter taste and crispness besides its jet black hue.
Black Diamond apples are a rare variety from the family of Hua Niu apples (also known as the Chinese Red Delicious). The name is a little misleading because they aren't exactly black, but rather a dark hue of purple.
The unique apples owe their color to their native geography in Nyingchi, a small city in the mountains of Tibet, where they receive a lot of ultraviolet light during the day but the temperature fluctuates dramatically at night, causing the skin to develop a deep, dark color. The flesh inside is white and bright like any other apple.
A farmer Norm Schultz explained that black apples are picked in the fall (when other apples are harvested) but they're quite tart right off the tree. After being stored for several months, they develop a sweeter taste and their hard flesh softens up making them much more enjoyable.
Although they offer a nice, sweet crunch, Black Diamond apples likely don't have a higher nutritional value than most commercial apple varieties.