Most people have seen rainbows - single or multiple - and connected with their symbolism and beauty.

I have many rainbow files posted on Crystalinks - science and pseudoscience.

In science ... A rainbow in science is a meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky. It takes the form of a multicolored arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the sun. Rainbows can be full circles; however, the average observer sees only an arc formed by illuminated droplets above the ground, and centered on a line from the sun to the observer's eye. Read more ...

Rainbow Breathing Whales Under the Golden Gate Bridge

From -- "Rainbow breathing whale" sounds like a mythical creature. On July 12th, Mila Zinkova of San Francisco saw one ... for real. She took this picture looking over the edge of the Golden Gate Bridge. "A few humpback whales crossed under Golden Gate Bridge and entered the Bay," says Zinkova. "Just then I saw their rainbow-colored sprays. It was beautiful!" This is not mythology. It's physics. When Zinkova took the picture, the sun was behind her back shining down into the droplet-filled exhaust of the whale's spout. Sunbeams reflecting from the water droplets produced a prismatic spray of color just like an ordinary rainbow. Of course it didn't look ordinary.

Metamaterial prism creates a reverse rainbow   PhysOrg - January 9, 2015
In a normal rainbow, red is always on "top" while violet is on the "bottom." This is true whether the rainbow is created by a glass prism or by water droplets in the sky, and is due to the way that these materials refract light of different wavelengths: colors with longer wavelengths (red) are less refracted/bent than colors with shorter wavelengths (violet). Now in a new study, scientists have designed a prism that does the opposite: it refracts longer wavelengths more strongly than shorter wavelengths. The result is a reverse rainbow.

In a "Rainbow" Universe Time May Have No Beginning   Scientific American - December 9, 2013
What if the universe had no beginning, and time stretched back infinitely without a big bang to start things off? That's one possible consequence of an idea called "rainbow gravity," so-named because it posits that gravity's effects on space-time are felt differently by different wavelengths of light, aka different colors in the rainbow. Rainbow gravity was first proposed 10 years ago as a possible step toward repairing the rifts between the theories of general relativity (covering the very big) and quantum mechanics (concerning the realm of the very small). The idea is not a complete theory for describing quantum effects on gravity, and is not widely accepted. Nevertheless, physicists have now applied the concept to the question of how the universe began, and found that if rainbow gravity is correct, space-time may have a drastically different origin story than the widely accepted picture of the big bang. According to Einstein's general relativity, massive objects warp space-time so that anything traveling through it, including light, takes a curving path.

Scientists Stop Light in 'Trapped Rainbow' Live Science - November 15, 2007
Scientists have worked out how to bring beams of light to a screeching halt inside a material that would separate the light into its constituent colors, creating a rainbow - a trapped rainbow. To bring light to a stop from its usual approximately 670 million mph (1.08 billion km/h) pace is no easy feat, and scientists have been working on the problem for years in hopes of revolutionizing how information is stored and sent. To tackle the challenge, physicist Ortwin Hess of the University of Surrey and his colleagues have devised a theoretical means to stop light using what are known as metamaterials, or materials whose properties depend on their structure and not the composition of the material.

The property of these materials that makes them ideal for stopping light is their "negative refractive index." The refractive index of a medium is a measure of how much light slows down and reorients or bends as it passes through the medium. Most materials, such as glass and water, have a positive refractive index - light keeps moving in basically the same direction. The negative refractive index of metamaterials (created by arranging tiny metallic inclusions in a transparent material) causes the light to bend somewhat back on itself and in such a way that "it gets slower and slower and eventually stops," Hess explained. (These same materials have been used to create an "invisibility cloak.")