Colour that ant becomes (3)
I believe the answer is:
tan
'colour' is the definition.
(I know that tan is a more specific form of the action colour)
'ant becomes' is the wordplay.
'becomes' indicates an anagram.
'ant' anagrammed gives 'TAN'.
'that' is the link.
(Other definitions for tan that I've seen before include "Lie in sun" , "Brown colour acquired from sun" , "Turn dark in sun" , "Go brown" , "function" .)