Basic colours (8)
I believe the answer is:
standard
This clue is a double definition.
'basic' is the first definition.
(similar in meaning)
'colours' is the second definition.
(I've seen this before)
(Other definitions for standard that I've seen before include "Normal - colours" , "Established model - flag" , "Flag - norm" , "Reference point, benchmark" , "Jack" .)