As manager of a breeding and training facility, I first read this book some years ago, and surprisingly, found myself disappointed with it. Just recently I reread this book, believing that perhaps it has more to offer than I had previously given it credit for. Sadly, I still cannot give it positive ratings.
Sponenberg is accurate on much of the genetics portion of this book. On color identification, however, he stands far below his fellow veterinarian/authors. The names he makes up for the various equine colors are ridiculous. Fellow breeders who read this most likely find it amuzing, if not insulting. To the unknowing, however, learning this information incorrectly can be detrimental to the attainment of this knowledge. Backyard breeders need to contact their breed society before employing the use of terms like these on their horses' registration papers. These are not toy poodles we're dealing with. "Cutesy" made-up names for common horse colors are not the mark of the professional breeder/registrar.
There are better books on this subject. Try "The Color of Horses: The Scientific and Authoritive Identification of the Color of the Horse" by Dr. Ben K. Green. It is well explained, easy to comprehend, direct, and professional. Though "The Color of Horses" was out-of-print for awhile, the high demand for this book has brought it back into publication.