The world of The Green Knight is filled surrealism and mist. there’s symbolism and metaphor with colours and texture which is striking and thrilling.
“We tried to be careful about the amount of green, and we often had a very ochre or a very blue version of green. It was just a little bit too heavy-handed, and also just aesthetically didn’t look that great. [Director of photography] Andrew [Droz Palermo] found that green turns into neon really quickly—the color of Slimer in Ghostbusters.” - David Lowery.
The green in the film is also a representation of the life cycle and morality, from birth to death and you'll notice the different shades of it used in these moments that represent the cycle.
“green is what is left when ardor fades, when passion dies, when we die, too.”