Variety of yellow crackers? Not quite (6)
I believe the answer is:
banana
'variety of yellow' is the definition.
(banana is a shade of yellow)
'crackers? not quite' is the wordplay.
'crackers?' becomes 'bananas' (both can informally mean mad).
'not quite' means to remove the last letter.
'bananas' with its last letter taken off is 'BANANA'.
(Other definitions for banana that I've seen before include "Yellow fruit with slippery skin" , "6 Yellow fruit" , "Fruit item" , "Fruit grown in hands" , "Small politically unstable country dominated by foreign companies" .)