A sort of colour relationship? (7)
I believe the answer is:
kindred
'relationship?' is the definition.
(I've seen this before)
'a sort of colour' is the wordplay.
I cannot really see how this works, but
'sort' could be 'kind' (synonyms) and 'kind' is found in the answer.
'colour' could be 'red' (red is a kind of colour) and 'red' is found within the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for kindred that I've seen before include "Related; similar in kind" , "Congenial" , "Family - similar" , "Family - like" , "Family and relations" .)