I had some time to spare yesterday while waiting for my train, so I popped in to the W H Smiths in Cambridge station.
As I was scanning a wall of best sellers, I noticed that my wandering eyes were drawn to those with the lightest covers.
However, when I switched to trying to read the titles, those with light text on a dark background became more prominent. (All these books were laid flat against the wall.)
Therefore, perhaps a good approach to book cover design is to have a light background colour and on this have a dark panel with light text for the title.
Perhaps a redesign is called for.