rainbow spectrum:notes is the second artbook by Toaru Majutsu no Index illustrator Haimura Kiyotaka containing his latest works. It was announced as part of the Kamachi Kazuma 10th Year Anniversary Celebration. It also includes an exclusive original short story written by Kamachi Kazuma, "Shinyaku Toaru Majutsu no Index SS". It is the sequel to Haimura's previous artbook rainbow spectrum:colors.