Unusual palette, including large bit of blood (8)
I believe the answer is:
platelet
'blood' is the definition.
(I've seen this in another clue)
'unusual palette including large bit of' is the wordplay.
'unusual' indicates anagramming the letters.
'including' indicates putting letters inside.
'bit of' suggests taking the first letters.
The initial letter of 'large' is 'l'.
'palette' with letters rearranged gives 'patelet'.
'patelet' placed around 'l' is 'PLATELET'.
(Other definitions for platelet that I've seen before include "Small disc in the blood" , "Cell fragment in the blood, important for clotting" , "Particle in blood involved with clotting" , "Disc-shaped blood cell" , "something in the arteries" .)