A box with a purplish red cover: metal (8)
I believe the answer is:
platinum
'metal' is the definition.
(I know that platinum is a metal)
'a box with a purplish red cover' is the wordplay.
I cannot quite understand how this works, but
'a' is present in the answer.
'box' could be 'tin' (I've seen this in other clues) and 'tin' is found within the answer.
The remaining letters 'plum' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for platinum that I've seen before include "Valuable stuff, after a grind" , "Precious metal; sort of blonde" , "Metal used in jewellery" , "Type of blonde; best-selling (record)" , "Heavy white metal" .)