Higher in rank, could become purple if learner included? (5)

I believe the answer is:

upper

I'm a little stuck... Click here to teach me more about this clue!

'higher in rank' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for upper that I've seen before include "Nearer the top" , "Amphetamine pill" , "form of stimulant" , "Part of a shoe; drug" , "catcher of swans?" .)

I've seen this clue in The Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.