Part of a Scottish loch, red in colour (5)
I believe the answer is:
ochre
'colour' is the definition.
(I know that ochre is a colour)
'part of a scottish loch red' is the wordplay.
'part of' indicates a hidden word.
'OCHRE' is hidden within 'scottish loch red'.
'in' acts as a link.
(Other definitions for ochre that I've seen before include "Red or yellow pigment" , "Golden pigment" , "Yellow-red earthy pigment" , "Chore (anag) - pale brownish-yellow" , "Earth coloured pigment" .)