Finish the race with an increase in colour (6)
I believe the answer is:
cerise
'colour' is the definition.
(cerise is a kind of colour)
'finish the race with an increase in' is the wordplay.
'finish' says to take the final letters.
'race with' becomes 'c' (I can't justify this - if you can you should give a lot more credence to this answer).
'an increase' becomes 'rise' (rise is a kind of increase).
'in' indicates putting letters inside.
The last letter of 'the' is 'e'.
'c'+'rise'='crise'
'e' placed within 'crise' is 'CERISE'.
Can you help me to learn more?
(Other definitions for cerise that I've seen before include "Light clear red" , "Reddish-pink colour" , "Pinkish red" , "Light red colour" , "Colour of ripe cherries" .)