Ship in an American shade: green (6)
I believe the answer is:
grassy
'green' is the definition.
(I've seen this before)
'ship in an american shade' is the wordplay.
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'in' means one lot of letters goes inside another.
'an american shade' becomes 'gray' (I can't explain this - if you can you should give a lot more credence to this answer).
'ss' inserted inside 'gray' is 'GRASSY'.
Can you help me to learn more?
(Other definitions for grassy that I've seen before include "Like lawns or pasture" , "Naturally green?" .)