Place covered in unmixed colour (6)
I believe the answer is:
purple
'colour' is the definition.
(purple is a kind of colour)
'place covered in unmixed' is the wordplay.
'place' becomes 'pl' (I've seen this in other clues).
'covered in' means one lot of letters goes inside another.
'unmixed' becomes 'pure' ('pure' can be a synonym of 'unmixed').
'pl' inserted into 'pure' is 'PURPLE'.
(Other definitions for purple that I've seen before include "Red and blue mixed" , "Mixture of red and blue" , "shade" , "Colour of the angry" , "Colour for aristocracy or emperors" .)