spectra

Quantum mechanics was initially developed to explain the atom, especially the spectra of light emitted by different atomic species. The quantum theory of the atom developed as an explanation for the electron's staying in its orbital, which could not be explained by Newton's laws of motion and by classical electromagnetism.
http://en.wikipedia.org/wiki/Quantum_mechanics
my ears perk up when ther's something about color - otherwise - so many words to click on and distracting for me - so I'm skipping back up a link