what was peculiar about the concert?

The sun is setting and Alec leads them out of Reality into the forest where an enormous symphony orchestra with over a thousand members are playing at once. A tall, thin man with dark, deep-set eyes conducts them without a baton. Milo is puzzled because he hears no sounds but Alex tells him that they are playing the sunset, which they do every evening. Each instrument plays a color and they all play throughout the day.

Many of the instruments stop playing as night descends and the conductor, whom Alec introduces as Chroma the Great, drops his arms. Milo compliments him and asks if he plays all day long. Chroma assents and says he rests at night but the musicians play on. When Milo asks what happens if they stop playing. Chroma shows him – everything becomes dull and lined like a blank coloring book. The world would be dismal without color, he states.