is a rainbow dark or bright colours
The longer wavelength coloured light, such as red, has a large rainbow angle, then the short wavelength colours, such as blue. The index of refraction of light in water is a measure of the speed of light in water. All colours, or wavelengths, do not travel at the same speed. primary rainbow is always somewhere on an arc 42 degrees around the shadow of your head (called the anti solar point). So the brightly illuminated rain must be in this direction away from you to see a rainbow. For a secondary bow it is 51 degrees around the shadow of your head.