Dogs are not completely colorblind, but they have dichromatic vision, meaning they see colors differently from humans. Dogs have only two types of color receptors (cones) in their eyes, which correspond to blue and yellow. Humans have three types of cones, allowing them to see red, green, and blue. As a result, dogs see the world mostly in shades of blue and yellow and cannot distinguish red and green well. Colors such as red may appear as yellowish brown to dogs, and green may appear as shades of gray or brown. This type of color vision is similar to red-green color blindness in humans.