Spread the last of the ochre in Tempera mix (8)
I believe the answer is:
permeate
'spread' is the definition.
'the last of the ochre in tempera mix' is the wordplay.
'the last of' indicates one should take the final letters.
'in' indicates putting letters inside.
'mix' indicates an anagram.
The final letter of 'ochre' is 'e'.
'tempera' is an anagram of 'permate'.
'e' going within 'permate' is 'PERMEATE'.
(Other definitions for permeate that I've seen before include "Flow or spread into every part of" , "Spread throughout" , "Percolate" , "Infiltrate" , "Suffuse" .)