Disclaimer: We don't own Loki or Thor. They belong to Marvel.
Red is the color of blood. Of anger, and battle. It suits Thor, one so quick to anger and drive his companions on the path toward war. But red is also the color of love, of caring and compassion. Thor fits this too, a man always willing to stand before others and take the hits so they don't have to. Loki never doubted the colour of Thor's cape. Just as he told himself he had never doubted that Thor still held love for him, that he would come back for him. Red always followed Thor, billowing around him in a majestic wave of scarlet.
Loki always clothed himself in emerald green. It is the color of the envy he felt, dodging the scarlet that nearly buffets him in the face. It empowered him in its own flood behind him as he sought to take a world for himself and it pooled beneath him as he clawed for a throne. Deep in his heart he told himself over and over that green was always the opposite of red.
How ironic that thought was now, after he had failed once more and been granted his punishment. The jailers had stripped him of his emerald cloak, taking the shattered remains of dignity with the tattered cloths. The emotions the color brought dissipated, greed and envy fled leaving him in his numb hole. How ironic that the man cloaked in emerald shadows would be brought into the light to find his skin painted with rivulets of crimson. Sometimes he would pretend the red flowing over him was Thor's cape, there to offer warmth and protection, but the trickster held no more strength to trick himself, the scarlet came too wet and slick and chilled. Loki hadn't thought he could still be shaken with cold, but shivering wracked him as ice flowed through his veins.
The lights were searing in their brightness, harsh and unfeeling. In individual bursts the darkness overcame the lights, growing stronger each time. In time it won, and Loki was forced to succumb to the shadows again. But now they no longer held familiar emerald, only black.
Thor stood shocked at the sight of the once proud man before him, now beaten and melted down to an unfamiliar display of horror. He dragged his scarlet cape down from about his broad shoulders and laid it upon the man before him. He shook as the form whimpered as the weight settled on cracked flesh and malformed limbs.
He settled the figure in his arms, feeling every bit as if he was still pulling a young child from the ruins of Midgardian buildings but forced every moment to recognize that the form curled into him was no child, only the broken pieces of what should have been a godly king.
In this, Thor made his promise to his brother.
Thor would return the emerald to Loki, would raise him to his glory. Green would return to him like the leaves and flowers in spring.