Sensitivity making everything turn grey (7)
I believe the answer is:
allergy
'sensitivity' is the definition.
(allergy is a kind of sensitivity)
'everything turn grey' is the wordplay.
'everything' becomes 'all' (all things).
'turn' is an anagram indicator.
'grey' with letters rearranged gives 'ergy'.
'all'+'ergy'='ALLERGY'
'making' is the link.
(Other definitions for allergy that I've seen before include "Hypersensitivity to a substance" , "Abnormal body reaction" , "Unfavourable reaction to, say, pollen" , "Unfavourable reaction to pollen, certain foods etc" , "Adverse reaction (med.)" .)