Dichromatism is a disorder. Our brains expect a trichromatic signal and when it only receives dichromatic information the hues are “repeated” because a cone (usually the one responsible for green) is not available. In people with green-weak color blindness this makes green look like a “weak” reddish hue. Tetrachromats’ brains are still expecting a trichromatic signal but they get more information than is expected. That means that the image contains more information or detail but the colors are not nee colors.