|My dog, Oscar|
In your eye you have special cells called rods and cones. When you see things, you're looking at light bouncing off of objects. The job of the rods and cones is to detect that light, and send the information to your brain.
Rods are very sensitive to light, but can't see color. They're what you use at night.
Cones only work in bright light, but they can see different colors. Since this post is about color vision (and whether dogs have it), I'll talk about cones for the rest of the post.
How color vision works:
|Visible light is a spectrum made up of all the colors|
You have three types of cones, each specialized for different colors: red, green, and blue. Red light activates the red cones. Purple light activates the red and blue cones. This is kind of like how mixing primary colors when painting creates new colors. The only difference is that in paint, the primary colors are red, yellow, and blue; but in light, the primary colors are red, green, and blue. Every color you see comes from the three cones being activated in different amounts, with the amount depending on the color. The cones talk to the brain. The brain calculates the different levels that the different cone types are activated, comes up with a result, and perceives it as color.
Some people only have two types of cones instead of three. These people are colorblind. The most common kind is red-green colorblind, where someone is missing either the red cones or the green cones, and has difficulty telling the difference between red and green. More rarely, people will lack blue cones, and have difficulty telling the difference between blue and yellow. Colorblindness is hereditary, and more likely to affect boys than girls.
|Rainbow - Normal color vision|
|Rainbow - Red-green colorblind|
|Rainbow - Blue-yellow colorblind|
How dogs see:
Dogs are red-green colorblind. We know this because 1) they have two cones types, and 2) when given vision tests, (with lots of yummy treats for motivation!) they can distinguish colors like red-green color blind people can. This means they can see colors, but they can't tell the difference between red and green.