A simple way to add color or pattern to a room is by lining the back of bookshelves. While one could paint these areas, another approach is to cover poster board or foam core cut to the appropriate size with fabric.
Looking closely at the above detail from a kitchen design by Mosaik Design, it appears this has been the approach taken here. And the best part of this simple DIY project? If you should tire of the fabric choice, simply remove or replace with another style.
To see a wonderful collection of rooms given a dose of personality through adding color and pattern to the walls behind bookshelves, built-ins and ledges, read my latest Ideabook on Houzz.