Rainbows can be seen in many places besides the sky. Maybe you’ve seen them in your sprinklers or reflected off of oil. This experiment explains why that is.
This experiment shows refraction. As light travels through thicker substances, it tends to slow down and give off a greater wavelength. The change in wavelength is what changes the color that gets reflected back to us. Since nail polish is thicker than air, refraction occurs. The nail polish gets thinner and thinner as it spreads across the water, so different wavelengths, and thus colors, are shown.