Unfading colour always seen on top (9)
I believe the answer is:
evergreen
'unfading' is the definition.
(thesaurus)
'colour always seen on top' is the wordplay.
'colour' becomes 'green' (greening is a kind of colouring).
'always seen' becomes 'ever' (I can't justify this - if you can you should give a lot more credence to this answer).
'on top' says to put letters next to each other (in a down clue, some letters go above others).
'green' after 'ever' is 'EVERGREEN'.
Can you help me to learn more?
(Other definitions for evergreen that I've seen before include "Scots pine, perhaps" , "Non-deciduous tree - always immature?" , "Star anise, say" , "box, perhaps" , "Holly, say" .)