Jacket starts off the uniform, newly in colour (5)
I believe the answer is:
tunic
'jacket starts' is the definition.
'tunic' can be an answer for 'jacket' (I've seen this before). I'm unsure of the 'starts' bit.
'the uniform newly in colour' is the wordplay.
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'uniform newly in colour' becomes 'unic' (this might be a standard abbreviation of which I'm unaware).
't'+'unic'='TUNIC'
'off' is the link.
Can you help me to learn more?
(Other definitions for tunic that I've seen before include "Policeman may be in one" , "Short uniform coat" , "Simple garment" , "Smock" , "Upper garment, for a soldier say" .)