Rainbow spectrum:colors

rainbow spectrum:colors is the first artbook by Toaru Majutsu no Index illustrator Haimura Kiyotaka and was released on February 28, 2011. It contains a collection of art from Haimura's light novel illustrations. The art book incorporates both color pieces and monochrome works in chronological order from Toaru Majutsu no Index, with shorter sections for other works like Maid DEKA and Sprite Spiegel. It also includes an interview, a tutorial, and an exclusive original short story written by Kamachi Kazuma "Toaru Majutsu no Index SS: Love Letter Competition".

A second artbook titled rainbow spectrum:notes was announced as part of the Kamachi Kazuma 10th Year Anniversary Celebration.

Toaru Majutsu no Index SS: Love Letter Competition
Featuring a new illustration by Haimura for the short story, the story follows the aforementioned letter that was sent by Kumokawa Seria to be given to Kamijou Touma as it changes hands between various characters from the series.