One of these four colors is not in the rainbow. Which one is it?

Who discovered the rainbow?

The Greek philosopher Aristotle first started musing about rainbows and their colours back in 350 BC. His ideas were picked up and elaborated upon by the Roman philosopher Seneca the Younger in his Book 1 of Naturales Quaestiones around 65 AD. Senaca was surprisingly ahead of his time in his reasoning, even predicting the discovery of the prism effect by Newton centuries later.

Throughout the ages, thinkers, philosophers and naturalists examined the phenomenon of the rainbow effect, noting its appearance not just in the sky but in other circumstances too.

But in every case, two elements were essential for that characteristic burst of colour, water vapour or droplets and sunlight. Finally, Isaac Newton proved that white light is made up of a spectrum of colours by splitting light with a prism. His discovery, together with the work of others before him, finally explained how rainbows form.

He also noted that the sequence of the colours of a rainbow never changed, always running in the same order. He coined the idea that there are seven colours in a spectrum: red, orange, yellow, green, blue, indigo and violet (ROYGBIV).