Taps into source of mineral pigment (5)
I believe the answer is:
ochre
'mineral pigment' is the definition.
(I've seen this before)
'taps into source' is the wordplay.
'taps' becomes 'ch' (cold and hot taps).
'into' is an insertion indicator.
'source' becomes 'ore' (I have seen 'Source of mineral ' mean 'ore' so perhaps 'source' could also mean 'ore').
'ch' placed within 'ore' is 'OCHRE'.
'of' is the link.
(Other definitions for ochre that I've seen before include "Earth coloured pigment" , "Orangey colour" , "Pale brownish-yellow colour or pigment" , "Yellowish-orange colour" , "What gives a yellow colour" .)