Via design*sponge – Domino magazine has a flickr group and one of the users – chotda has arranged her bookshelf according to color. It looks awesome, but I'd go crazy trying to find things… I'm forgetful as is. I arrange alphabetically mostly (it falls apart when I run aout of space). Here is a flickr group – rainbow of books were others have arrange their books according to color.
And back in 2004, artist Chris Cobb rearranged the entire contents of Adobe bookstore in San Francisco by color. The work was entitled "There is Nothing Wrong in This Whole Wide World". Here's a link to an NPR broadcast about this with a slideshow of pictures, and another link with some lovely photos taken by a blogger at superhero designs. A couple of pictures from those sites below: