Brown ant running (3)
I believe the answer is:
tan
'brown' is the definition.
(I know that tan is a type of light brown)
'ant running' is the wordplay.
'running' is an anagram indicator.
'ant' with letters rearranged gives 'TAN'.
(Other definitions for tan that I've seen before include "Tawny" , "belt" , "Curry" , "Brown to beat" , "Prepare leather" .)