Rainbow v Library: organising books

I find magazines a great source of inspiration. I also like flicking through them - having them at my fingertips on my iPad is, for me, pure heaven. 

Although the photo* below isn't my style I was drawn to it by the bookcase. It is the way I'd organise my wardrobe - by colours - and I like the effect in this room. But would I approach a bookcase in the same way, it got me thinking...

Initially I thought this was way too organised and OCD-like, even for me. But then the alternative (and how our bookshelves usually look) is to have books grouped together by topic (travel, fiction, crafts and so on) and to have those mostly in alphabetical order. I'm not sure now which is worse... Or most OCD-like...

How do you organise your bookshelves?



* Photo credit: from August 2013 Ideal Home