The missing quality that makes for conspicuousness (7)
I believe the answer is:
absence
This clue might be a double definition.
'the missing quality' is the first definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'for conspicuousness' is the second definition.
The definition and answer can be both states of affairs as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'that makes' acts as a link.
Can you help me to learn more?
(Other definitions for absence that I've seen before include "Failure to attend" , "Seen cab (anag.)" , "Abstraction" , "Cause of fonder heart?" , "Need" .)