Gold container — on the inside black and a sort of red (6)
I believe the answer is:
auburn
'a sort of red' is the definition.
(reddish colour)
'gold container on the inside black' is the wordplay.
'gold' becomes 'au' (Au is the chemical symbol for gold).
'container' becomes 'urn' (urn is a kind of container).
'on the inside' means one lot of letters goes inside another.
'black' becomes 'b' (as in pencil classifications).
'au'+'urn'='auurn'
'auurn' going around 'b' is 'AUBURN'.
'and' acts as a link.
(Other definitions for auburn that I've seen before include "Name of Goldsmith's deserted village (6)" , "Reddish-brown hair colour" , "Golden" , "Shade of brown" , "Copper" .)