Boy in blue and reddish-brown (6)
I believe the answer is:
copper
'brown' is the definition.
(I know that copper is a type of Venetian red)
'boy in blue and reddish' is the wordplay.
'boy in blue' becomes 'cop' (I've seen this in another clue).
'and' is a charade indicator (letters next to each other).
'reddish' becomes 'per' (I can't justify this - if you can you should believe this answer much more).
'cop'+'per'='COPPER'
Can you help me to learn more?
(Other definitions for copper that I've seen before include "Part of force" , "An element; small coin" , "Metal - washing-machine?" , "A reddish-brown metal" , "Little money" .)