I had ordered William Powell's Color Mixing Recipes for Portraits from Amazon several months ago...and really like it. After seeing this book on a stand at my local art supply store, I went ahead and bought it without first taking the time to look through it thoroughly in the store. I wish now that I had. In my opinion, way too many pages are devoted to showing the color tint changes based upon adding more, and more, and then some more, white into a particular color. For my purposes, it would have been better served to perhaps include only 1 or 2 representative tints with white for many colors, rather than the six big color swatches included for just a handful. For instance, it might be useful to see which dark reds could be tinted to produce the particular type of pink you're looking for. However, as an example, the entirety of page 21 shows the various tints that can be achieved by adding 5 slightly increasing amounts of titanium white to 3 separate colors (venetian red, burnt umber, and burnt sienna). Once you've seen the resultant tint by adding white to venetian red, you can pretty much guess what it's going to look like when you add a smidge more white. A number of pages are taken up by this...which, to me, wastes quite a bit of space considering there are only 26 pages of actual recipe information in the book. It wouldn't be an issue if this were a more extensive book; but, as it is a minimal-page book to start with, it seems that these pages are being used simply as "filler" and at the sacrifice of more worthwhile pages. While I didn't really expect that the book would contain recipes for every type of color combinations (heck, I can certainly make my own "mud"); I did expect much more than what it contained. There were so many great color mixes that it overlooked...including some of the beautiful greys and earth tones. Okay, I'll step down from my soapbox now.
As with his other paint recipe books, the spiral binding is a great addition. There are 5 pages of "value" recipes in the book which I found sort of useful...the rest not so much. Otherwise, there is a bit on color theory in the front and a small section on portrait painting in the back, but that information is simply an abbreviation from his portrait book that I already own (and highly recommend). For those folks just learning to mix colors, this book might be helpful for its abbreviated color theory alone...but, for the color mixes, you can also make your own useful charts (using the paints you already have or want to buy). See below.
Since I paint in oils, I make charts out of canvas paper and use Q-tips instead of brushes when painting the sample swatches (If you're doing dozens of color combinations, it's a pain to have to keep cleaning out brushes to keep the colors pure). I write the paint colors that I own down the side and also across the top of the canvas paper (sort of like a grid). I then put a small "speck" of each oil paint in its respective place across the grid (there will be 2 colors at each spot on chart). Using Q-tips, I blend each color combination into a decent-sized "swatch." Those colors that seem nice, but too dark, I'll add a bit of white to tint it enough to truly "see" the color result. You'll end up with a few swatches that are simply "mud"...not interesting at all...but don't overlook some of the beautiful greys and browns that result from mixing colors that are complements of one another. For example, mixing alizarin crimson and sap green results in a lovely rich mahogany color. I now have a few pages of canvas paper charts that I can refer to when I'm looking for a specific color.
UPDATE: I've noticed that Powell has a new color recipe book (published 2012) that is supposed to contain over 1,500 color combinations. It's sold on Amazon for just several bucks more (at the time of this review). While it's hard to see exactly what you're getting when you click on the "Look Inside" Amazon feature, it does look like it is probably a more worthwhile book.