An orange was a common Earth citrus fruit that could be eaten or juiced.
The phrase apples and oranges usually refers to differences between two situations. Commander Charles Tucker III used this reference when comparing his rank to that of Sub-commander T'Pol. (ENT novel: Broken Bow)
Aren't you a bag of oranges and morning sunshine? was a phrase used by New Zealand native Commander Veronica Fletcher to Captain Erika Hernandez in 2155. (ENT novel: Kobayashi Maru)
In 2269, Spock believed that an orange was a more useful gift than a rose, so he gave Katalya Tremain a dwarf orange tree. (TOS novel: Vulcan!)
The USS Enterprise sensors could distinguish the difference between apple trees and orange trees while several kilometers above a planets surface. (TOS novel: Crossroad)
Wesley Crusher was given the nickname of orange from his friend Jaan Devin in 2365. (TNG novel: Strike Zone)