Blues, reds, purples, greens, and browns make this a much more interesting area than just a flat black. As you look further down his chest, you see the shadow growing darker, but there is still a great deal of color other than black.
One of the other things that makes the black interesting is the patterns in his fur. He had been playing and was wet so the fur really clumped together to make the patterns stand out. One of the things that seems to really help the animal look themselves is capturing the fur correctly.
The other detail shot is of his front and back left feet. Here the colors are cooler. The shadow and light areas are still captured, but there is not as much detail in the fur. This also gives you a closer look at the grass.
By using the masking around his feet, I was able to lap the grass over his feet giving the impression his feet were further down in the grass and hidden. On the right side of his front leg you'll notice a slightly lighter edge to the leg. This gives it dimension and keeps it from blending in to the back leg. It's subtle and really not noticeable unless it's pointed out, but it helps the image to read correctly.