Sort of red spy man shortly arrests (7)
I believe the answer is:
magenta
'sort of red' is the definition.
'spy man shortly arrests' is the wordplay.
'spy' becomes 'agent' (I've seen this before**).
'shortly' means to remove the last letter.
'arrests' indicates putting letters inside.
'man' with its last letter taken off is 'ma'.
'agent' placed within 'ma' is 'MAGENTA'.
(Other definitions for magenta that I've seen before include "Light mauvish-crimson" , "Purplish-red - battle" , "Colourful" , "Bright purplish red or magnate" , "Light purplish-red" .)