Teenage Sung-woo's family continuously adopts a new child to fill in for his brother who went missing a decade ago. Fending off emotional intimacy with his boyfriend to protect a truth that might turn him away, finally Sung-woo finds someone to share his secret with.

Dong-min, an art major who is completely colorblind, must submit an assignment on his favorite color. As he works on the project with his crush, Kyung-jun, he struggles to grasp the sky blue that Kyung-jun loves. In the process, Dong-min begins to listen to his own heart.