How Rainbows Are Made ?

There are two raindrops illustrated on the image.

The droplet with the light rays depicted with colored, solid lines has the long wavelength (red) ray going into the observer's eye. The blue ray depicted by the solid line does not enter the eye. The rain drop with the light rays depicted with colored, dashed lines has the short (blue) wavelength ray going into the observer's eye. The long wavelength (red) depicted by the red dashed line does not go into the eye.

Only one wavelength from a rain drop makes it into the eye. But there are many rain drops, in many different positions and because light will interact with each rain drop in the same way, there is steady progression from long wavelengths (red) near the top of the rainbow to short wavelengths (blue) near the bottom of the rainbow with the yellow and green colors in between.

When we see a rainbow be aware that the entire sky is loaded with raindrops. Yet, we see only a narrow band of color we call a rainbow. That is because the eye receives only a narrow band of rays from a narrow band of raindrops. None of the other light rays reflected from the other raindrops make it into our eyes from the particular position we are in at any one time.