What part of speech is the colors change on leaves in fall?

This is a phrase rather than a single word. Here's how the parts of speech break down:

* The colors: This is a noun phrase acting as the subject of the sentence.

* change: This is a verb, the main verb of the sentence.

* on leaves: This is a prepositional phrase acting as an adverbial modifier, telling us where the change occurs.

* in fall: This is another prepositional phrase acting as an adverbial modifier, telling us when the change occurs.

Overall, the entire phrase "the colors change on leaves in fall" functions as a clause, specifically the main clause of a sentence.