Green hair, like red-heads, have sexual connotations. Green is more serene and associated with birth and sexual satisfaction. Green is all about completion and wholeness. Reds are more focused on the desire for sex than birth and completion. That is why Greens and Reds are complements of each other. Like the colors, the personalities are slightly at odds yet also fit together. Greens cannot have the cycle of reproduction they are often associated with without the lust of the Red.
Greens are passive. Darker greens feel a lot more exotic than lighter greens. The color is also considered trustworthy. Interestingly, very dark shades of green are associated with disease and illness.
Characters of this color are sometimes highly sensual, but at the same time, they are not sexual. They hint and suggest but never act. These characters often have supportive roles in the story. A good example is C.C. from Code Geass. She assists the protagonist Lelouch in his efforts to fulfill the contract he has with her. Being immortal, she represents the endless cycle of life and death. She is also highly sensual; she spends a lot of time taunting Lelouch with leg, too-tight clothing, and suggestive poses. Yet, she never entices action.
Another example of Green is Eureka from Eureka Seven. She is an interesting character. She is passive at times, but she is also a strong active character in her own right. In the show, she is an “Eve” in many regards. She even adopts 3 orphans to further support the reproduction cycle her archetype represents. In the series, she can also see/read energy called Trapars that swirl throughout her world. It is useful when piloting planes and mechas that use these energy streams to fly. Eureka is also very sensual; unlike C.C, she isn’t aware of her sensuality. Her body type is very feminine, and she sometimes poses herself in provocative ways to emphasize this unconsciously. Late in the story, she is severely scarred and takes a while to heal. Green’s healing abilities isn’t only for others.
Like all hair colors, not all greens show these characteristics. There are greens that act more like reds or even blondes. A favorite of this type of turn-about is the green haired library girl who has a wild/red side that comes out over time.
Green is one of the more exotic hair colors. Despite being the color of nature, characters that are otherworldly or simply alien in the UFO sense of the word have this color. The play between the serene trustworthy feelings the color invokes and the unsettling “wrongness” or extra-terrestrial feelings is a favorite with authors.
Another good example of green that came to mind while reading this is Roronoa Zoro of One Piece. Despite his “wild” image and reputation as a physically strong pirate/ex-bounty hunter, he has a very calm and collected disposition. He’s also very loyal to Luffy and is often the one to knock some sense to the rest of the crew whenever something wrong happens, like an internal dispute or confusion over their situation.
Greens often play stabilizing roles. I wonder if character designers consciously use hair as shorthand or if color and archetype association is unconscious.