Detective dressed in blue and brown (5)
I believe the answer is:
sepia
'brown' is the definition.
(I know that sepia is a type of brown)
'detective dressed in blue' is the wordplay.
'detective' becomes 'pi' (private eye).
'dressed in' means one lot of letters goes inside another (inserted letters are dressed in others).
'blue' becomes 'sea' (I can't explain this - if you can you should believe this answer much more).
'pi' placed within 'sea' is 'SEPIA'.
'and' is the link.
Can you help me to learn more?
(Other definitions for sepia that I've seen before include "Sort of ink" , "Brown tint" , "Brownish tint or pigment" , "Reddish-brown colour - easy as pie" , "tone of pictures?" .)