"what may well be the world's foremost research program on comparative color vision....Over a series of some 4,000 trials, each dog was taught to "find the one that's different"....dogs do see color, but in a more limited range than that seen by normal humans, who see the rainbow of colors described by "VIBGYOR": Violet, Indigo, Blue, Green, Yellow, Orange, and Red (plus hundreds of variations on these shades). Instead, dogs see "VIBYYYR" (Violet, Indigo, Blue, Yellow, Yellow, Yellow, and Red). The colors Green, Yellow, and Orange all look alike to dogs; but look different from Red and different from the various Blues and Purples. Dogs are very good at telling different shades of VIB apart. Finally, Blue-Green looks White to dogs.
The simple explanation for these differences in color vision is this. The retinas of normal humans have three (3) types of color receptors, called "cones". Each cone type is particularly sensitive to light of a narrow limit within the entire VIBGYOR range. That means that three different "cone lines" of communication run back to the visual part of the brain, which then compares the weight of the signals coming in from each of cone "line". Different weights produce a perception of different colors. In dogs (and in "green-blind" humans), there are only two (2) types of cones, so there is less basis for comparison by the brain, and thus the perceived color range is more limited. In sum, dog color vision is "color-limited", not "color-blind".
http://www.puplife.com/dogcaretips/howdogsseecolors.html
"Can Dogs See in Color?
It is not true that dogs are completely colorblind. While dogs do not have the same color vision as humans, they are able to tell yellow from blue. Like a human with red-green colorblindness, they are unable to tell the difference between red and green.
The reason for this limited range, in both the colorblind human and the dog, is that there are only two kinds of color receptors in the retinas of their eyes. While most humans have three kinds of color cells, with three different receptor molecules sensitive to blue, greenish-yellow, and red, dogs only have receptors for yellow and greenish-blue. Canine eyes also lack another human trait: the fovea, an area especially dense with detail-sensing cells. As a result, their detail vision is not as good as ours. But they make up for this by having much better night vision and greater sensitivity to movement."
http://www.discountpetmedicines.com/dog-health-blindness-color-dog.htm
The common belief that dogs are color blind is false. Dogs can see color, but it is not as vivid a color scheme as we see. They distinguish between blue, yellow, and gray, but probably do not see red and green. This is much like our own vision at night. Dogs' eyes have large pupils and a wide field of vision, making them really good at following moving objects. Dogs also see well in fairly low light."
http://www.i-pets.com/petfunt-dog.html
" Dogs can see in much dimmer light than humans. At twilight when you are having trouble seeing shades of color, they see as well as what you were seeing at noontime. Dogs can detect motion better than humans can. Dogs do not have the ability to focus as well on the shape of objects (their visual acuity is lower). An object a human can see clearly may appear to be blurred to a dog looking at it from the same distance. A rough estimate is that dogs have about 20/75 vision. This means that they can see at 20 feet what a normal human could see clearly at 75 feet. Dogs are said to have "dichromatic vision" -- they can see only part of the range of colors in the visual spectrum of light wavelengths. Humans have "trichomatic vision", meaning that they can see the whole spectrum. Dogs probably lack the ability to see the range of colors from green to red."
http://experts.about.com/q/700/3616856.htm
"Dogs can see in much dimmer light than humans. This is because the central portion of a dog's retina is composed primarily of rod cells that "see" in shades of gray while human central retinas have primarily cone cells that perceive color. The rods need much less light to function than cones do.
Dogs can see flickering light better than humans. The only significance to this appears to be that dogs may see television as a series of moving frames rather than as a continuous scene.
Dogs do not have the ability to focus as well on the shape of objects (their visual acuity is lower). An object a human can see clearly may appear to be blurred to a dog looking at it from the same distance. A rough estimate is that dogs have about 20/75 vision. This means that they can see at 20 feet what a normal human could see clearly at 75 feet.
Dogs are said to have dichromatic vision -- they can see only part of the range of colors in the visual spectrum of light wavelengths. Humans have trichomatic vision, meaning that they can see the whole sprectrum. Dogs probably lack the ability to see the range of colors from green to red. This means that they see in shades of yellow and blue primarily, if the theory is correct. Since it is impossible to ask them, it is not possible to say that they see these colors in the same hues that a human would. Whether or not the ability to see some color is important to dogs or not is hard to say.
http://www.vetinfo.com/dogsee.html
"To test if my dog was color-blind, I first trained him to choose blue over yellow. I chose blue and yellow because they appear very different when viewed in a grey scale. After my dog was trained to choose blue, I tested him to see if he could still choose blue over red because it is almostidentical to blue when viewed in a grey scale. My dog chose the blue over the red 72% of the time. Since my dog was able to chose the blue over the red 72% of the time, I concluded that my dog is not completely color-blind."
http://66.102.7.104/search?q=cache:...4/Projects/J1003.pdf+are+dog+colorblind&hl=en
"Dogs are [somewhat] 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."
http://www.uwsp.edu/psych/dog/LA/DrP4.htm
"Dogs appear to be better than people with peripheral vision, but their close-up vision does not seem as sharp as a human's. This is due in part to the placement of the eyes in the dog's skull. The dog's lateral eye placement allows better wide-angle vision but hinders depth perception and close-up viewing because there is minimal visual overlap (binocular convergence) between the two eyes. Hence, your dog can easily snag a ball moving sideways but may have trouble catching a ball tossed right at his nose.
The structure of the dog's retina helps explain other idiosyncrasies of canine vision. Abundant light-sensitive cells called rods in your dog's retina help it detect motion and see well in dim light - clear advantages for canines stalking prey at dusk or dawn or guarding territory against intruders. In contrast, the human retina is made up predominantly of cones - receptors that are better at detecting color and processing bright light. Contrary to popular belief, dogs are not completely colorblind for they do have cones in their retinas. But dogs can't distinguish the full spectrum of colors.
The tapetum lucidum is another ocular structure that gives canines enhanced ability to see in dim light. This thin, reflective tissue is part of the choroid layer, which lies behind the retina. The tapetum reflects light back through the retina, giving the retina a second opportunity to absorb light. You may be more familiar with the function of the tapetum lucidum than you think: it's what causes the bright reflection from a dog's eyes when car headlight shine on them at night."
http://www.cah.com/dr_library/eyedog.html
