Technologically advanced green must accept progress (5-3)
I believe the answer is:
space-age
'technologically advanced' is the definition.
(I've seen this before)
'green must accept progress' is the wordplay.
'green' becomes 'sage green' (shade of green).
'must accept' means one lot of letters goes inside another.
'progress' becomes 'pace'.
'sage' enclosing 'pace' is 'SPACE-AGE'.
(Other definitions for space-age that I've seen before include "Futuristic" , "Ultra-modern" .)