Faint-hearted Tory with this becomes Green (6)
I believe the answer is:
yellow
'green' is the definition.
(yellow green is a kind of green)
'faint-hearted tory with' is the wordplay.
'faint' becomes 'yell' (I can't explain this - if you can you should give a lot more credence to this answer).
'hearted' indicates the central letters.
'tory' becomes 'con' (abbreviation for Conservative).
'with' becomes 'w' (abbreviation).
The middle of 'con' is 'o'.
'yell'+'o'+'w'='YELLOW'
'this becomes' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for yellow that I've seen before include "Flaxen" , "See 15" , "Colour of egg yolk and cowardice" , "Sort of hammer, jersey or belly" , "Colour of cowardice, custard" .)