Tint of marine coats particularly intense at first (5)
I believe the answer is:
sepia
'tint' is the definition.
(I have seen 'Brown tint ' mean 'sepia' so perhaps 'tint' could also mean 'sepia')
'marine coats particularly intense at first' is the wordplay.
'marine' becomes 'sea' (both can mean 'of the sea').
'coats' is an insertion indicator (inserted letters are coated in another word).
'at first' indicates taking the first letters.
The initial letters of 'particularly intense' is 'pi'.
'sea' enclosing 'pi' is 'SEPIA'.
'of' acts as a link.
(Other definitions for sepia that I've seen before include "Colourant" , "Reddish-brown colour - easy as pie" , "Dark reddish-brown pigment" , "Old drawing" , "Reddish-brown colour as in old photos" .)