In one of his most famous experiments, Isaac Netwon, with characteristic brilliance, proved that the colours emanating from a prism when white light passed through it were not, as some suggested, created by the prism itself, but were already present within the light. He did this by passing individual colours emerging from the prism through a second prism and showing that the colour of the resultant light remained unchanged.
Driving towards work last week, I saw a remarkable natural recapitulation of Newton's experiment.
I was heading west along the motorway, when the sun appeared above the horizon directly behind me, and its first rays created a rainbow in front of me. But the early-dawn Rayleigh scattering of the sunlight had filtered out the other colours of the spectrum, leaving the sun's rays a spectacular, primary red. So, when the rays encountered the rain shower in front of me, there were no other colours left within them to be refracted and reflected by the raindrops, meaning that the resultant rainbow was an unusual, monochromatic red.
Sorry there are no photographs to show you, but I was doing 70mph at the time!
The effect only lasted for a short while. As the sun climbed in the sky, it returned to its more usual colour, and the colours of the rainbow were restored.