Humans and old world monkeys have three different types of cones (trichromatic vision) while other mammals lack cones with red sensitive pigment and therefore have poorer (dichromatic) colour vision.

• 人和高等的灵长目动物有三种不同的视锥细胞，而其它哺乳动物缺乏对红色的视锥细胞，因此它们对颜色的分辨比较差。