Missing column is yellow (9)
I believe the answer is:
spineless
I believe this clue is a double definition.
'missing column' is the first definition.
('column' can be 'spine' (I have seen 'Vertebral column ' mean 'spine' so perhaps 'column' could also mean 'spine') so maybe 'missing column' can be ''spineless')
'yellow' is the second definition.
(I've seen this before)
'is' acts as a link.
(Other definitions for spineless that I've seen before include "Yellow" , "Weak; invertebrate" , "Lacking (moral) courage" , "Not like Mrs Tiggy-Winkle" , "Craven, lacking vertebrae" .)