Used a bland grey, mostly (2,3,5)
I believe the answer is:
by and large
'mostly' is the definition.
(I know that mostly can be written as by and large)
'used a bland grey' is the wordplay.
'used' indicates an anagram.
'a'+'bland'+'grey'='ablandgrey'
'ablandgrey' is an anagram of 'BY AND LARGE'.
(Other definitions for by and large that I've seen before include "In the main" , "In general" , "Speaking generally" , "for the most part" , "As a rule" .)