The distribution of Light or a signal spread out by wavelength and frequency; sunlight split into colors by a prism is the classic example.
Helium was discovered on the Sun before on Earth. During an 1868 eclipse, astronomers found an unknown yellow line in the solar Spectrum; Norman Lockyer named the new element after Helios. It was not isolated on Earth until 1895.
Purple does not exist in the light spectrum. When red and blue light simultaneously stimulate the eye, the brain creates this color to resolve the contradictory signals.