Your Eyes (слэш)

Steve has been dealing with his crush on Bucky for a long time, and the war hasn't been the best for their relationship. When Bucky asks Steve to watch the sunset with him, who's he to say no? He doesn't have a clue that he'll find one of the biggest shocks of his life.
Based on the prompt: You see in black and white until you kiss your soulmate, and the first color you see is their eyes. After that, everything becomes in color until your soulmate dies.