Suggest wearing primarily colourful unknown fabric (6)
I believe the answer is:
chintz
'fabric' is the definition.
(chintz is a kind of fabric)
'suggest wearing primarily colourful unknown' is the wordplay.
'suggest' becomes 'hint' (synonyms).
'wearing' is an insertion indicator.
'primarily' suggests taking the first letters.
'unknown' becomes 'z' (algebra).
The first letter of 'colourful' is 'c'.
'c'+'z'='cz'
'hint' going into 'cz' is 'CHINTZ'.
(Other definitions for chintz that I've seen before include "Printed multi-coloured cotton fabric" , "Shiny cotton fabric used for furnishings" , "Printed and glazed cotton fabric" , "Printed, patterned cotton fabric" , "Patterned fabric for soft furnishings" .)