It may come as a shock the purple hue at the bottom of the rain bow, is not the bluest light that has been bent at the largest amount, but a superposition of a "Supernumerary" rainbow. The darker blue at the short wavelenght is being mixed with the red of the next rain bow. I have not been able to model this effect. The supernumeray rainbows are seen when the rain drop size are close to Mie white cloud scattering.
Here is another picture which to the untrained eye looks as if the last colour of the rainbow is purple, but you can see it is very light green.
If you put sunlight through a prism you get the pictures below
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