Rainbow is beautiful, natural and meteorological phenomen which inspire people in many ways.
It is caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky.
Sir Isaac Newton was a pioneer in research on light. He subdivided the spectrum he observed into five colors- red, yellow, green, blue and violet. Later he included orange and indigo. That was a consequence of his interest in alchemy and the ancient Greeks who had a bit of an obsession with number seven.
Today the rainbow inspire scientists to further explore the nature of color and light.