What causes rainbow colors in the sky? Not a 'rainbow' but the colors high in the sky.?

Answer 1

perception of color is the function of cells on the retina called cones. each human cone has one of three pigments in it that responds to a narrow range of wavelengths of light. any one pigment can't determine what wavelength of light it has absorbed so the brain compares the responses it receives from each cone to construct a color image.

Answer 2

I've read that Jews and Christians believe that god(s) placed a rainbow in the sky as a promise he/they (holy trinity) would not flood the earth again. More scientifically minded folk understand that even if all the ice melted on the earth there is not enough water to cover the surface of all land masses, hence Noah did not need an Ark but a good pair of rubber boots and a raincoat. Second, scientifically minded folk know rainbows not signs from god(s) but instead are the dispersion of sunlight that is refracted by tiny water droplets in the form of mist or rain. Sir Issac Newton replicated this phenomenon in the 1600s when he used a refractory prism to disperse sunlight.