Book covers, revisited

Just spotted that Tim is busy working on something that I dabbled with last February:
www.colourphon.co.uk
I’m actually in the midst of revisiting my code, as I want to automate a way of locating visually similar images from the “1000 Frames of Hitchcock” project, e.g.:

Anyway, today seemed like a good opportunity to return to Ed Vielmetti‘s original question about sorting books into the colour of a rainbow…