It is caused by both reflection and refraction of light in water droplets, thus resulting a rainbow/spectrum of multiple colours in the sky.
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Actually white colour is formed by all the seven colours. VIBGYOR all these colours gives white colour when they mixed. Rainbow is formed on dispersion of light. V: violate I: indigo B: blue G: green Y: yellow O: orange R: red.
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2.8degrees.rainbow is formed only after the rain if there is sunshine. after the rainatmosphere is filled with water droplets,it act like smallprisms.when sunlight falls on this waterdroplets it undergo refraction and multiple reflection and then emergedout.when light undergo refraction.light dispersed and we get allthe 7colours.its formed between 40.8degrees and 42.8degrees light get dispesed according to the wavelength of the colours.higher the wavelength lower the deviation.