Sensitivity makes 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' (I've seen this before).
'turn' is an anagram indicator.
'grey' with letters rearranged gives 'ergy'.
'all'+'ergy'='ALLERGY'
'makes' is the link.
(Other definitions for allergy that I've seen before include "unhealthy reaction" , "Hypersensitive reaction to certain substances" , "Cause of ill-feeling" , "Unfavourable reaction as to pollens or foods" , "Strong aversion" .)