About 500 may be Communist (3)
I believe the answer is:
red
'be communist' is the definition.
(red can informally mean communist)
'about 500' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'500' becomes 'D' (Roman numeral for 500).
're'+'d'='RED'
'may' acts as a link.
(Other definitions for red that I've seen before include "Colour of blood" , "Florid" , "Left-wing" , "Colour of garnets" , "Bordeaux claret, for instance" .)