Colours of crude undies donned by this person (3,6)
I believe the answer is:
oil paints
'colours' is the definition.
(colours used for painting)
'crude undies donned by this person' is the wordplay.
'crude' becomes 'oil' (I've seen this before).
'undies' becomes 'pants' (underpants).
'donned by' means one lot of letters goes inside another.
'this person' becomes 'I' (the person writing).
'pants' enclosing 'i' is 'paints'.
'oil'+'paints'='OIL PAINTS'
'of' is the link.
(Other definitions for oil paints that I've seen before include "Painter's media" , "Artist's pigments" , "Artist materials" , "What some artists use" .)