I stack mine in chronological order, from the oldest to the most recent. The smallest books are on the first shelf, and the bound volumes and larger books are on the bottom, with some on the middle shelves.
Was the colour coding due to the average witness not being much of a reader?
I think it may have been more of a selling ploy. The colours of the books were used as a way of catching the eye of the householder. And I'd dare say that the colours changed in order to differenciate the latest books from the others. Back in the 70s, I remember at least two books would be released at the annual conventions, so that might have been another reason - so you knew straight away which book was which.
Sphere - they certainly don't print pics like that anymore!! Nowadays Eve is discreetly covered by her own long hair and/or the surrounding foliage.