Dogs are believed to see blue nuances the best. They also see greenish-yellow, yellow, and different shades of gray. That means a blue toy can pop and be extra fun, but a red ball will have about the same color as the green lawn.
While they may be missing out on the bright red, dogs can see a wider range of pastels and sepias than a human, and they can distinguish between shades of gray that look the same to us.
They may also be able to make out different types of light than we can see, and many theorize that dogs can see the ultraviolet spectrum. And, they see much better in low-light conditions than we do. Dogs see almost as well in darkness as cats.
Another interesting thing is that dogs are near-sighted. Their vision is believed to be grainy, and that makes it harder to distinguish details at a distance. They do have a wider field of vision than we do. Most humans have a field of vision of 180 degrees, cats see 200 degrees, and most dogs around 240 degrees.