Spread throughout the last of the ochre in tempera mix (8)
I believe the answer is:
permeate
'spread throughout' is the definition.
(I've seen this before)
'the last of the ochre in tempera mix' is the wordplay.
'the last of' says to take the final letters.
'in' indicates putting letters inside.
'mix' indicates anagramming the letters.
The last letter of 'ochre' is 'e'.
'tempera' with letters rearranged gives 'permate'.
'e' put within 'permate' is 'PERMEATE'.
(Other definitions for permeate that I've seen before include "Spread or pervade" , "Infiltrate" , "Imbue, spread through" , "Suffuse" , "Percolate" .)