Before contents of churn in addition turned bright yellow (7)
I believe the answer is:
sulphur
'bright yellow' is the definition.
The answer and definition can be both related to change as well as being verbs in their base form.
Perhaps you can see a link between them that I can't see?
'before contents of churn in addition turned' is the wordplay.
'before' says to put letters next to each other.
'contents of' indicates the central letters (the letters on the inside of the word).
'in addition' becomes 'plus' (synonyms).
'turned' shows that the letters should be reversed in order.
The middle of 'churn' is 'hur'.
'plus' backwards is 'sulp'.
'hur' put after 'sulp' is 'SULPHUR'.
Can you help me to learn more?
(Other definitions for sulphur that I've seen before include "Highly flammable yellow element" , "S (chem.)" , "Element, atomic no. 16" , "Chemical used in match heads" , "Chemical element" .)