Reddish-brown uniform packed in trunk with books (8)
I believe the answer is:
chestnut
'reddish-brown' is the definition.
(I've seen this before)
'uniform packed in trunk with books' is the wordplay.
'uniform' becomes 'U' (phonetic alphabet: alpha, bravo, charlie etc.).
'packed in' is an insertion indicator.
'trunk' becomes 'chest' (I've seen this before).
'with' means one lot of letters go next to another.
'books' becomes 'NT' (New Testament).
'chest'+'nt'='chestnt'
'u' going within 'chestnt' is 'CHESTNUT'.
(Other definitions for chestnut that I've seen before include "Wood" , "Conker tree - 11 of 10" , "Tree fruit known informally as a conker" , "not a cracker!" , "Horse coat colour" .)