Dogs are red-green color blind. They see a brighter and less detailed world when compared to humans. Peripheral vision is better than humans (dogs see more of the world), but distance is not judged quite as well. Dogs excel at night vision and the detection of moving objects. Figure 1 is a rough guesstimate of what a dog and human might see when viewing a color band (the electromagnetic spectrum).
These differences in visual ability make sense in light of evolutionary theory. Good depth perception and visual acuity are necessary for a primate (from which humans evolved) jumping from tree limb to tree limb. Good color vision enabled this primate to choose the ripest and most nutritious fruit. The canine, on the other hand, is well adapted as a nocturnal hunter of camouflaged prey.