Light gets refracted every which way in a rainbow thru water droplets in the air - depending on the wavelength of light and the angle it passes thru a water droplet. But, in the center of the rainbow, refracted wavelengths or colors combine with refracted colors from other droplets to make white light again. That's why the center of a rainbow is often brighter than the surrounding sky. The bands of colors we think of as a rainbow are just the edge where colors are refracted at angles that don't combine with other colors.