Perfect for when I'm going through a fit of the blues (7)
I believe the answer is:
sublime
'perfect' is the definition.
(thesaurus)
'through a fit of the blues' is the wordplay.
'through' means one lot of letters goes inside another.
'a fit' becomes 'im' (I can't justify this - if you can you should give a lot more credence to this answer).
'of' indicates anagramming the letters (the answer comes from or 'of' the letters).
'blues' anagrammed gives 'suble'.
'im' inserted within 'suble' is 'SUBLIME'.
'for when i'm going' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for sublime that I've seen before include "Wonderful" , "Heavenly" , "Exalted, lofty" , "Glorious; supreme" , "Exalted; awesome" .)