Tone down adult clues for this? (4)
I believe the answer is:
blue
'tone down' is the definition.
'blue' can be an answer for 'down' (thesaurus). I'm unsure of the 'tone' bit.
I don't understand how the rest of the clue works.
(Other definitions for blue that I've seen before include "ball at snooker" , "Dismal" , "Sad, squander" , "as the sky, perhaps" , "Colour of depression" .)