Range of colourings allowed having spread around (7)
I believe the answer is:
palette
'range of colourings' is the definition.
(eg a painter's palette)
'allowed having spread around' is the wordplay.
'allowed' becomes 'let' (to let is to allow or permit).
'having spread' becomes 'pate' (I can't explain this - if you can you should give a lot more credence to this answer).
'around' means one lot of letters goes inside another.
'let' put inside 'pate' is 'PALETTE'.
(Other definitions for palette that I've seen before include "Artist's paint mixing board" , "Board for an artist" , "Painter's utensil" , "Painter's board" , "colourful board?" .)