Showy decoration lacking hint of nuance (6)
I believe the answer is:
garish
'showy' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for garish that I've seen before include "Showy, lurid" , "Hag, sir, could be gaudy" , "Loud" , "Gaudy, lurid" , "Bright and showy" .)