Nuances one's got to have a clear head to see (9)
I believe the answer is:
'nuances' is the definition.
(I've seen this before)
'one's got to have a clear head to see' is the wordplay.
'got' is an insertion indicator.
'have' is an insertion indicator.
'a clear' becomes 'ver' (I can't explain this - if you can you should believe this answer much more).
'head to' says to take the initial letters.
The initial letter of 'see' is 's'.
'one' placed around 'to' is 'otone'.
'otone' enclosing 'ver' is 'overtone'.
Can you help me to learn more?
(Other definitions for overtones that I've seen before include "added nuances" , "subtle innuendoes" , "Subtle implications" , "Upper partials" .)