Empty scarlet and green tube (5)
I believe the answer is:
straw
'tube' is the definition.
(I know that straw is a type of tube)
'empty scarlet and green' is the wordplay.
'empty' says to hollow out the word (remove centre letters).
'and' says to put letters next to each other.
'green' becomes 'raw' (both can mean naive or inexperienced).
'scarlet' with its middle taken out is 'st'.
'st'+'raw'='STRAW'
(Other definitions for straw that I've seen before include "Disastrously, it may be the last" , "Remains of corn" , "Animal bedding" , "Thin tube; yellow" , "trifle" .)