Uniform is black trousers, ready to supply (8)
I believe the answer is:
issuable
'ready to supply' is the definition.
I can't judge whether this definition defines the answer.
'uniform is black trousers' is the wordplay.
'uniform' becomes 'U' (phonetic alphabet: alpha, bravo, charlie etc.).
'black' becomes 'sable' (heraldic term for black).
'trousers' is an insertion indicator (to trouser can mean to steal or take).
'is'+'sable'='issable'
'u' inserted into 'issable' is 'ISSUABLE'.
Can you help me to learn more?
(Other definitions for issuable that I've seen before include "Fit to be put out" , "Fit for publication" .)