Maroon maybe about 500 (3)
I believe the answer is:
red
'maroon' is the definition.
(I've seen this in another clue)
'about 500' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'500' becomes 'D' (Roman numeral for 500).
're'+'d'='RED'
'maybe' acts as a link.
(Other definitions for red that I've seen before include "Carmine" , "Colour of garnets" , "Scarlet or vermilion" , "14 -- breed of 4" , "lefty" .)