Whenever people talk about dog eyesight, it’s often written off as dogs being broadly color blind. Which is then interpreted as dogs don’t actually see in color, which gets compounded more when some TV show or movie shows the point of view of a dog in black and white. Is this actually true, though? Does being color blind really mean dogs see in black and white?
Rods and Cones
The eyeball is complex–both yours and your pet dog’s. Inside your eyeball are three types of photoreceptor cells: rods, cones, and photosensitive retinal ganglion cells. You’re probably the most familiar with rods and cones. The first one is for your vision when it’s dark and the second is for when it’s light out. Rods don’t play a very significant role in color vision, and by that we mean they have almost no role in color vision–which is why it’s so much harder to make out colors in the dark. What rods do have on cones is sensitivity. Rods can react to stimulation as little as a single photon.
Anyway, cones. Instead of just responding to light in general, cones respond differently to different wavelengths of light. Those different responses allow you to perceive color. The average person has three different types of cones, each sensitive to differing ranges of wavelength. This gives us trichromatic vision where you can perceive blue (short wavelength), green (medium), and red (long) pretty well. You also get to blend them together, so you can perceive colors in between like orange or yellow.
Color blindness broadly changes how this works, sometimes limiting the wavelengths you can perceive because you either lack the requisite cones or the cones you do have react differently from the average persons’. You probably know color blindness doesn’t mean you see no color, it’s more common that those with color blindness simply cannot distinguish between certain colors (like blues and greens or reds and browns). It is possible to have total color blindness where you perceive no color at all. It’s called achromatopsia.
If you’re wondering if trichromatic vision is the upper limit, it’s not. The mantis shrimp is a dodecachromat, wherein it has 12-16 receptors. Some people have tetrachromatic vision, meaning they have four different types of cones. Tetrachromacy is more common in fish, birds, reptiles, and insects than it is in mammals.
So, does your dog suffer from achromatopsia? Probably not. Dogs are dichromatic, which means they have two types of cones. Where humans can see the combinations of red, green, and blue; dogs get blue and yellow. If you wanted to approximate it with a color blindness simulation, you’d want to look for a red-green colorblindness simulation (deuteranopia). When dogs were tested for their reaction to colors, they responded most similarly to people with deuteranopia. The visual acuity of domestic dogs is also roughly a third of humans in both bright and dim light.
See if you’re good with alternate color uses here.