Why do people think that dogs are color blind?

People often think dogs are color blind because they see the world differently than humans do. While humans have three types of color receptors (cones) that allow us to perceive a wide range of colors, dogs have only two types, which makes their color vision similar to that of a human with red-green color blindness. This means they primarily see shades of blue and yellow but have difficulty distinguishing between reds and greens. However, dogs are not completely color blind; they simply experience a more limited color palette.