Particular colour noticed in Loch Restil (5)
I believe the answer is:
ochre
'particular colour' is the definition.
(ochre is a colour)
'noticed in loch restil' is the wordplay.
'noticed in' says the answer is hidden in the clue.
'OCHRE' can be found hidden inside 'loch restil'.
(Other definitions for ochre that I've seen before include "paint type" , "Orange-yellow colour" , "Yellowish-brown or red pigment" , "Yellow-orange pigment" , "Yellowish-orange colour" .)