It’s because of the color of chemical light. In the lyrics she is singing, there is a phrase : “Lemon Iro no Tsuki no Shizuku Atsumete, Anata no Yuku sono Michi wo Yasashiku Terashi te Itai” The meaning of this is “I wanna illuminate your future by the color of Lemon.” In her concert, participants are always using pink color chemical light because that is the color which fits her image. But participants want to illuminate her future, by the color of Lemon, which is the same as Lyrics! So participants choose the different color. She saw that at the concert. That’s why she is crying.
@@ChaosMissile Thank you for replying! My English is awful, but I’m very happy if someone who doesn’t use Japanese can understand how moving the scene is! That’s my little wish :)