Statesboro, GA, USA
There is a serious flaw in this question for anyone with english/ grammar 101.
Why is an orange?
This is either inaccurate in word choice or it is missing something in order to be a valid question.
You can say "why is an orange orange?"
You can even say "why is there an orange?"
or "why are there oranges?"
or "why do oranges exist?"
But the bottom line is that (no matter how you tell us not to think about it and to just answer it), this question makes no grammatical sense as it stands.
The closest I can figure, you are dancing aroud the question of existence which is legitimate... but this is worded absolutely wrong.
To answer the question concerning existence, I would say that God created oranges for his own aesthetic pleasure and ours, for our nourishment (not his own), and that we might become aware of the power and wisdom of his nature.