WordPress book for graphic designers?

Is there a good WordPress book intended for graphic designers? I’ve started working with a friend in an arrangement where he designs a site and I build it in WordPress. This works great since I have the design sense of a blind monkey. He would like to learn more about WordPress and how best to design for it. I’m familiar with several good WordPress books, but most of them are intended for designer/developers. I’m looking for something that will serve as a guideline, offering suggestions for design conventions that are well suited to WordPress. Are there any such books? If there’s not a book specifically aimed at designers, which other book would you suggest?

Some said this rockable book is awesome, though I don’t buy it myself. I’m backend wordpress developer not front end, so I guess this book is not for me.