The colours of rainbow are known as the spectrum of light i.e. VIBGYOR ( V-violet, I-indigo, B-blue, G-green, Y-yellow, O-orange, R-red ). The process of formation of rainbow is splitting of white light into its component colours when is passes through a prism it is called dispersion. During the formation of rainbow the prism is considered as the water droplets and the transparent beam of light is the sunlight and it disperse through the water droplets which creates the spectrum of light which is called the rainbow.
Rainbow is a natural spectrum appearing in the sky after rain shower. As we know that the sunlight dispersed through the water droplets present in the atmosphere which act as a prism. A rainbow is always formed in the direction opposite to that of the Sun. The sunlight when passes through the water droplets it refract and disperse the incidence sunlight, then reflect it internal and finally refract it again when it comes out of the rain drop. Due to the dispersion of light and internal reflection different colours reach the observers eyes.