This book differs from a lot of other plant identification books in that it details them in order of colour. That may sound a bit odd, and not suit knowledgeable botanists, but for the novice trying to identify a wild flower with no previous knowledge it's a really useful book.
There are plenty of good photographs and illustrations with enough botanical text to work out what's what.
It's also small enough to carry around with you when you go for a walk and it's helped me identify plants countless times.