I am completely OCD about arranging things via colours of the rainbow. See?
Note that the shelf ends in the purples/reds and then goes into purple flowers. I'm not entirely happy with this yet, because it's hard to decide on a few of the orders... do I work with the patterning colours? I've got 4 more books to add to the collection (and if anyone knows where I can get War & Peace with the cover done by Coralie Bickford-Smith, I'd be thrilled), so that'll throw everything off too.
Need a closer look?
I stack cups and plates that way too. It's a problem.