A rainbow is an optical and meteorological phenomenon that is caused by reflection of light in water droplets in the Earth's atmosphere. This immense, curved spectrum of light appears only when both the elements of sunshine and rainfall present.
If the sun, the eye, and the center of the rainbow's arc are not in a straight line, the show is over, before it began. This explains why we only see rainbows in the early morning or late afternoon…it is physically impossible for us to align our eyes with the sun at other times of day, as it is high above our heads! Logically, a morning rainbow appears when the sun shines in the east, and the rain falls in the west, and an afternoon rainbow appears when the sun shines in the west, and the rain falls in the east.
THE SEVEN MAIN COLORS