Green wall up, having bit of a kip inside? (8)
I believe the answer is:
immature
'green' is the definition.
(I know that green can be written as immature)
'wall up having bit of a kip inside?' is the wordplay.
'wall up' becomes 'immure' (I've seen this before).
'having' is an insertion indicator.
'bit of a kip inside?' becomes 'at' (I can't justify this - if you can you should give a lot more credence to this answer).
'immure' placed around 'at' is 'IMMATURE'.
Can you help me to learn more?
(Other definitions for immature that I've seen before include "Not yet fully grown or developed" , "Undeveloped - unripe" , "Lacking in development" , "behaviour of child" , "Young" .)