It's for putting on colour (5)
I believe the answer is:
green
'colour' is the definition.
(I know that Green is a type of colour)
'it's for putting on' is the wordplay.
I cannot quite see how this works, but
'on' could be 're' ('on' can be mean 'with reference to') and 're' is found in the answer.
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for green that I've seen before include "Politician perhaps" , "right environmentally" , "Area around a golf hole" , "personification of envy" , "bowlers here?" .)