Red is dark to dogs, so they can’t see red. Green to them is white. So they are actually red-green blind. The light-sensitive cells of the retina consist mainly of cone cells and rod cells. The cone cells work in bright light and are mainly used for daytime vision and the important function of color recognition. Different cones can perceive different colors of light. Dog types have smaller cone cells in the retina than humans and can only tell colors in a portion of the wavelength range, such as blue, yellow, gray, etc., but can perceive variations in light and dark of each color, such as light blue, light blue, light yellow, etc. The dog also does not have red and green cones, so it is like the red and green blindness of the Blue Star. Dogs have larger pupils, a wider field of vision, higher levels of rod cells in the retina, and greater photosensitivity (rod cells can sense low light), so night vision is much better than in humans, and the eyes can adapt to movement more. Perhaps what we can’t see at night, dogs can easily see. Dogs can distinguish colors better than we can. Maybe we look like a lot of the same yellow, but there are ten different yellows in a dog’s eyes.
