All right, if it's not too dark (4,6)
I believe the answer is:
fair enough
'too dark' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'all right if it's not' is the wordplay.
I cannot really understand how this works, but
'right' could be 'r' (common abbreviation) and 'r' is located in the answer.
'not' could be 'no' (negative) and 'no' is found in the answer.
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for fair enough that I've seen before include "understandable" , "Very well" , "OK?" .)