Dragonfruit

Pitaya fruit, pitahaya fruit, commonly known as the dragon fruit, is a fruit from Central America, South America, and Asia. It has a light sweet taste, an intense shape and colour, and has a texture of between that of a kiwi and an apple. In addition to being tasty and refreshing, it contains a lot of water and other important minerals with varied nutritional ingredients.
Occurrence.
It is also known as “pitaya” if it comes from the very closely related Stenographers genus. The actual dragon fruit is the fruit of the cactus genus Hylocereus. Occuring in Mexico, South America, as well as Central America. It is possible it was introduced to Southeast Asian nations through Vietnam, alongside trade with the French during the 1800s. Cambodia, Thailand, Taiwan, Vietnam, and the Philippines, where it still holds as an important part of their diet. 
Yellow Pitaya.
The dragon fruit in the photo above. The yellow skin has white flesh. It has the highest sugar content among dragon fruits. In Chinese, it is called giraffe family and is commonly found in Hong Kong. The ripe ones are really sweet like sugar. 
References.
https://www.producebluebook.com/know-your-commodity/dragon-fruit/