Dogs are not color-blind like previously assumed, they can see colors, just not all colors.
Color comes in red, blue, and green spectrums.
Canines have a type of color-blindness called deuteranopia, meaning they lack the ability to discern the green spectrum. While dogs do recognize some red, it’s really the blue spectrum they’re best at detecting.
This selective color-blindness makes some sense in their world, as meat eaters, green things are just a distraction, a background to what’s important to them.
They’re looking for other dogs and things to eat, so they’d want to see reds and tans, black, gray, and white, and leave the greens to the herbivores.
Still, back to your question: if they don’t see greens, yellows, and some reds very well, then how are dogs taught to lead blind people through intersections?
That’s easy, it’s not the color changes that the dog watches for, it’s the position of the lights and the changes in the direction of the traffic that signal to the dog when it’s safe.
For a pedestrian crosswalk, a dog is taught to wait until the bottom light comes on, the one most of us see as green, and cross traffic is stopped before leading its owner across the street.
Sight for Poor Eyes.