The Tiny Bird & The Colors

The Tiny Bird & the Colors (ことりとりいろいろのいろ, Kotori Tori Iro'iro no Iro) is a book mentioned in the Black★Rock Shooter anime.The book is stated to be about "a bird that takes people to a world of different colors".

Description
In Mato's world, it was clearly popular enough to merit having more than one edition printed, also suggesting that it may be a very old book.

Mato is extremely fond of this book, to the point where she reads it over and over again and has a phone charm of the eponymous Tiny Bird. Yomi Takanashi also seems to be interested; she has a copy of the first edition, and drew a picture based off of a picture on the cover of the first edition to serve as her phone wallpaper. She later sends this picture to Mato.

The basic description is that the bird traveled to many different worlds and absorbed colors into its wings, such as "the blue of tears", "the pink of sneezes", and the "orange of smiles". However, it still wished to travel to new worlds, and it eventually absorbed so many colors that its wings became dull and black, dying in the end.

Trivia

 * Yomi's phone wallpaper is avaliable for download in Goodsmile Company's mobile site, here.
 * All of the colours described in the book, such as "the blue of tears", "the orange of smiles" and "the red of anger" are the theme colours of the "other selves" which appear in the anime.