Black Diamond apples are a rare breed of apples grown in the mountains of Tibet. They have a unique dark purple skin.
Black Diamond apples are a breed of Hua Niu apples (also known as Chinese Red Delicious) that get their unique dark purple color from the geographical conditions of Nyingchi, in the Tibet Autonomous Region. The 50-hectare orchard set up her by Chinese company Dandong Tianluo Sheng Nong E-Commerce Trade Co., Ltd. has an elevation of 3100 meters above sea level, making it the ideal place to grow these intriguing fruit. The temperature differences between day and night are significant, and the fruits get a lot of sunlight and ultraviolet light which causes their skin to go from the characteristic deep red of Hua Niu apples, to dark purple.
Source: Black Diamond Apples – The Rare, Dark Fruits You’ve Probably Never Heard Of