Oranges aren't naturally occurring fruits

[Costas]

Oranges are unknown in the wild. They are a hybrid of tangerines and the pomelo or “Chinese grapefruit” (which is pale green or yellow), and were first cultivated in south-east Asia. They weren’t orange, but green, and Vietnamese oranges and Thai tangerines are still bright green on the outside and orange inside.

https://www.telegraph.co.uk/men/the-filter/qi/8345477/QI-Quite-interesting-facts-about-orange.html