A lot of people are under the misconception that dogs don’t see colors, but they do. So how can we be so sure?
In the back of the eye is the retina, which works like film that used to be used in a camera, it has different layers and components. The parts that are sensitive to light are the photoreceptors. The two main components of the photoreceptors are the rods and cones. Because lots of research has been done on rods and cones we know that the rods function mainly in dim light and provide black and white vision, while the cones are responsible for detecting color.
Humans usually have three kinds of cones, where dogs have two. Most humans have cones that are sensitive to short, medium and long wavelengths of light, where dogs only have short and medium, not long or red. So because we know that cones are sensitive to color, we know that dogs see color, but not red, like we do.
Dogs also don’t see as clearly as we do, so roughly, a dogs sees what we do only blurrier and with no red.