Check inside mineral source for pigment (5)
I believe the answer is:
ochre
'for pigment' is the definition.
(ochre is a colour)
'check inside mineral source' is the wordplay.
'check' becomes 'ch' (abbreviation).
'inside' indicates putting letters inside.
'mineral source' becomes 'ore' (I've seen this before).
'ch' inserted into 'ore' is 'OCHRE'.
(Other definitions for ochre that I've seen before include "Yellow/brown pigment" , "Orange" , "Orangey colour" , "Orange-yellow colour" , "Golden pigment" .)