If you want it mainly for reading books, keep the black-and-white model. Battery life is far longer (long battery life is what the black and white displays were designed for), and I prefer a device that does the book reading job really well to a jack-of-all-trades that sacrifices that function just to do other things best done by other tools.
Only get color if you want web-browsing, photos, software apps, and the like on the same device. If you do want all those functions in one package, IMO, a tablet computer with an ebook reader app is a better choice because it has a better quality, larger screen.
FWIW, I use a black-and-white Kindle with the mini keyboard. The keyboard is good enough to take short notes and make highlights while you read. It only need charging about once a month; no problem with the battery not lasting through a long plane flight. If needing a reading light is a problem (such as for reading in bed), the same kind of LED clip-on reading light you can use on a paper book will work for the e-book reader.
