Green is the colour of his nightmares, the colour that brings a cold sweat to his skin.
Those eyes are always there to taunt him when he closes his eyes, always mocking him when he wakes from the nightmares with the smell of blood and fear tingling in his nose. Green eyes were his favourite before Loki, something that he associated with trust and with friendship because he saw them when he looked at Natasha, but now green reminds him of the madman and nothing good comes to mind when he thinks of him. Now he can barely look his partner and best friend in the face because he doesn't trust how he will react if her eyes meet his own.
There are times when he lies awake in the dark, the presence of his partner at his side, and he is sure that he can feel Loki creeping around inside his skull. He questions himself, tries to unsee the things that are slowly but surely coming back to him, and wonders whether sometimes the Asgardian is able to see through his eyes, whether he is watching, planning his next move, popping the cork on memories that Clint does not want to carry for the rest of his life just because he enjoys seeing how it affects them all. Sometimes he wonders whether his mind will ever really be his own again. He wonders whether he will ever wake up and believe, even for a second, that Loki is gone for good.
His fears aren't just for himself. He worries about the team-mates he has found in the Avengers, knowing that each and every one of them held back on nothing more than Natasha's word that she could break a god's control over him. Not one of them have ever made him believe that he is at fault for what happened to all of them. Not one of them has reminded him in word or deed that for a short time, entirely against his will or no, he was the enemy. Nobody reminds him that he led the attack in which one of their own died. He is thankful for them, every one of them and he does what he can to show them this.
The biggest fears that he has though are about the Russian assassin who sticks by him no matter what. Natasha, he knows, is the reason that he is alive, she is the reason that he has free will and independent thought once again. Perhaps he is a fool but he doesn't fear her because she is deadly, but because rather than keeping out of his way when he was a danger to everyone he knew, she put herself squarely in his path. She doesn't flinch from him, doesn't run from him, not even when she should. The sight of her eyes as she fought with him on the carrier, as she felt the bite of his knife at her throat, wakes him as often as the echoes of Loki's laughter.
Green is the colour that haunts him, two pairs of green eyes owned by very different people, one pair his destruction and the other his salvation. One he will never forget, the other he can never make it up to. He will never look into Natasha's eyes again without remembering what passed between them on that walkway inside the SHIELD carrier, he will never forget the vile and vicious thoughts that had circled his mind when he looked at her that day. No matter how far or how fast he runs from the past, it will always be there with him, just for a second, when green eyes meet his own. She doesn't judge, doesn't blame, she's forgiven him everything and she's still at his side, but Clint knows that those days when one man turned him against her will always be between them as long as he lives.
For Natasha green is the colour of the shadows in her own eyes, the colour of envy. She's lost count of the number of men who fall under her spell, captivated by the honeyed words that fall from her lips. She was the debutante of the Red Room, the example to which all others were held. She was the prodigal daughter, always on top, always victorious and always hated. Green is the colour of her own self hatred.
Green is also the colour of the Hulk. Try as she might, she's never been able to forget that she was the one sent to drag Banner into the mess that was New York, that her words and actions ended the longest calm spell that he's had since his accident. She brought him to the carrier; she had promised him that he wouldn't have to see action with the Avengers and the words turned out to be a lie. That she believed it all at the time doesn't matter; she was wrong. The Black Widow, always so sure of herself, always weighing the odds and winning, was reckless and overconfident that day and they both paid for it. They both pay for it still.
In the darkest of her dreams she can still hear his bellows as he chases her through the carrier. She can still feel the shaking of the ground beneath her feet and the thundering of her heart as she runs for her life, glass and sparks falling around her like rain. Sometimes, just before she wakes, she can remember the way he looked at her right before he changed, oh the pain in those eyes, the knowledge that he would have little to no control over what came next but would have to live with it regardless. That was the moment she found communion with Bruce Banner, in that moment she would have done anything to spare him what would come. He expected to come back to himself and find her body broken at his feet. She had looked at him and known that whatever happened next she was no match for him, that her body was only human, her skill set reliant primarily on hand to hand combat and the ability to manipulate others. Natasha makes a living from controlling the behaviour of others with words but there is no reasoning with the Hulk, only rage and the uncontrollable urge to smash whatever stands in his path. She had feared him then, she fears him still.
Occasionally the memories twist; she dreams that Thor did not get there in time to save her and Loki won. Sometimes she dreams that by bringing Banner aboard to help find her partner, she destroyed a part of one of the finest men she knows. Even now when Bruce looks at her she can see the apology in his eyes and she wonders if he can see one in hers. It wasn't his fault, it wasn't hers. It happened, they have to move on, look to the future, see things through.
Green is not a colour that brings her peace, it is the colour of their greatest weapon and the constant danger beneath their own roof.
Green is the colour of nightmares and both she and Clint see it regularly.