A slight semblance of change - how sad! (6)
I believe the answer is:
shadow
'a slight semblance' is the definition.
'shadow' can be an answer for 'semblance' (shadow is a kind of semblance). I am not sure about the 'a slight' bit.
'change how sad' is the wordplay.
'change' indicates anagramming the letters.
'how'+'sad'='howsad'
'howsad' anagrammed gives 'SHADOW'.
'of' is the link.
Can you help me to learn more?
(Other definitions for shadow that I've seen before include "opposing counterpart" , "It's cast when light is blocked" , "Air of gloom" , "Dark area, weak remnant (of something)" , "Follow; partial darkness" .)