As a former film student, I really should have commented on the cinematography - but yes, it's deliberately muted and you can see in the screencaps how carefully each shot is framed. I'm especially fond of the Garnet point of view (eg. through the bars of the crib in the scene with Ed toward the end). It gives the film a kind of askew view, i think. Puts it a little off centre.

And definitely one of Callum's best performances. He was right to be proud. :)