Kill Peter Rabbit

Young Incheon keeps a strange diary where not a single word is written... He lives by his own strict schedule, is deathly afraid of using public transport, adores the Marvel "Avengers" and the story of Peter Rabbit. He is autistic and cannot speak, read, or write. And it just so happens that Incheon becomes the only witness to a brutal double murder committed in the mental health center where he is being observed... Of course, no verbal testimony can be obtained from such a witness. All Incheon can do is color sheets of paper with different hues. And this is clearly not nonsense, but a clue pointing to the murderer. But how do you crack such an unusual cipher?