No that is stupid. Books should be ordered by subject and/or author. They are books, not decorative objects.
Though I DO love rainbows and colors. Pretty sure that is why I liked rocks and stamps and comics as a kid. First art I entered in an art contest was a large 6-8" wide clam shell with repeating rows of color, sort of like a rainbow, painted inside. I got a 3rd place ribbon. Probably around 1st or 2nd grade.