It's rather a colourless affair, mind (4,6)
I believe the answer is:
grey matter
'it's rather a colourless' is the definition.
I can't tell whether this definition defines the answer.
'affair mind' is the wordplay.
I cannot quite understand how this works, but
'affair' could be 'matter' (synonyms) and 'matter' is found in the answer.
The remaining letters 'grey' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for grey matter that I've seen before include "Intelligence; the brain" , "stuff in the head" , "intellectual capacity?" , "Brain tissue" , "Issue lacking clear boundaries" .)