Nigel regularly wears red to blend in (9)
I believe the answer is:
commingle
'blend in' is the definition.
'commingle' can be an answer for 'blend' (commingling is a kind of blending). I am not certain of the 'in' bit.
'nigel regularly wears red' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'wears' means one lot of letters goes inside another.
'red' becomes 'commie' (I've seen this before).
The alternate letters of 'nigel' are 'ngl'.
'ngl' going inside 'commie' is 'COMMINGLE'.
'to' is the link.
Can you help me to learn more?
(Another definition for commingle that I've seen is " Mix, blend".)