Through studies it has been suggested that an average dog sees similar to a human that is red-green colorblind.  Consequently, the dog's world consists of yellows, blues, and grays.  When a human perceives a red object it appears as yellow to the dog, while a green object appears as white, a shade of gray.  This white region, also called the neutral point, occurs around 480 nm in visual spectrum.  According to the electromagnetic spectrum, 480 nm would appear as a greenish-blue hue.  All wavelengths longer than the neutral point are indistinguishable from one another to the dog and would all appear as yellow.

Figure 1 shows two electromagnetic spectrums (from Dr. Plonsky, 1998).  The top spectrum is what the dog is able to perceive, and the bottom is what a human would perceive in the visible spectrum (wavelengths from 380 to 760).

 

Figure 1

The dog's ability to see detail, also termed acuity, is around six times poorer than an average human.  Acuity, measured in cycles per degree, is how many lines that can be seen as distinct entities in the visual field.  Humans have the ability to see about 30 cycles per degree while dogs can see about 12.