Colour one may be putting on (5)
I believe the answer is:
green
I believe this clue is a double definition.
'colour' is the first definition.
(I know that Green is a type of colour)
'one may be putting on' is the second definition.
(I've seen this before)
(Other definitions for green that I've seen before include "Environmentally concerned" , "Colour of malachite" , "Proverbial constituent of our moon" , "Ecologically correct" , "part of the golf course" .)