Pair oddly seen in marine tint (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')
'pair oddly seen in marine' is the wordplay.
'oddly seen' indicates alternate letters (letters in odd-numbered positions are used).
'in' indicates putting letters inside.
'marine' becomes 'sea' (both can mean 'of the sea').
The alternating letters of 'pair' are 'pi'.
'pi' inserted into 'sea' is 'SEPIA'.
(Other definitions for sepia that I've seen before include "Reddish-brown; cuttlefish ink" , "brownish colour" , "Colour from cuttlefish ink" , "Brown colour of old photo" , "cuttle" .)