View missing yellow hat (6)
I believe the answer is:
panama
'hat' is the definition.
(panama is a kind of hat)
'view missing yellow' is the wordplay.
'view' becomes 'panorama' ('panorama' can be a synonym of 'view').
'missing' indicates named letters should be taken away.
'yellow' becomes 'or' (heraldic term).
'panorama' with 'or' removed is 'PANAMA'.
(Other definitions for panama that I've seen before include "Style of hat" , "Hat; Central Am. canal" , "'Country, canal and hat (6)'" , "Criticise" , "city" .)