Brownish-yellow section of brooch revealed (5)
I believe the answer is:
ochre
'brownish-yellow' is the definition.
(I've seen this before)
'section of brooch revealed' is the wordplay.
'section of' indicates the answer is hidden within the clue.
'OCHRE' is hidden in the letters of 'brooch revealed'.
(Other definitions for ochre that I've seen before include "Earth used in pigments" , "Chore (anag) - pale brownish-yellow" , "Chore using pale brownish colour (5)" , "natural colouring" , "What gives a yellow colour" .)