It's much like I remember the Peterson Guides' (though it has been decades since I pored over them on summer vacations): In a style I would call more graphic than photorealistic, perhaps even a touch old-fashioned (although I think these are computer art, not gouaches), concentrating on silhouettes and feather masses. It also uses the Peterson Guide style of little arrows pointing to significant anatomical points, and includes in-flight (occasionally swimming) silhouettes and size guides compared to a modern male human silhouette.
The coloring is, I think, mostly hypothetical. There is an interesting discussion early on of how colors manifest in feathers, and why these early birds probably did not have really bright yellow, orange, red or green feathers, or bright red, orange, or yellow beaks.
The book is print-on-demand on matte paper, so the colors are somewhat subdued. They do look more natural that way.
It is really interesting to see a page of related creatures all together. What I find really interesting are the not-even-remotely-birds (*not* a technical term and probably rather unfair to the creatures). I had wondered how feathered dinosaurs would look and there is something pleasantly "of course" about these.