One opposed to having colonist on top of column (4)
I believe the answer is:
anti
'one opposed to' is the definition.
(I've seen this in another clue)
'colonist on top of column' is the wordplay.
'colonist' becomes 'ant' (I've seen this in another clue).
'on top of column' becomes 'i' (I can't justify this - if you can you should believe this answer much more).
'ant'+'i'='ANTI'
'having' acts as a link.
Can you help me to learn more?
(Other definitions for anti that I've seen before include "Policy's opponent" , "(Person who is) not in favour" , "Negative vote" , "one opposing?" , "Naysayer" .)