How can absorbed light cause a molecule to display a particular color?

The color of a molecule is a human observation of the inverse of its visible absorption spectrum. When a molecule absorbs specific wavelengths of visible light, it promotes an electron from a lower-energy molecular orbital to a higher-energy, unoccupied orbital. The energy difference ($\Delta E$) between these orbitals determines which frequencies of light are absorbed.12

The perceived color is the light that remains after the molecule has absorbed its characteristic frequencies. For example, a compound that absorbs light in the violet-blue region will appear yellow to the eye.12

The ability to absorb visible light often depends on the molecule's structure:
* Conjugated systems: Many organic compounds with extensive systems of conjugated $\pi$ bonds absorb visible light, which can result in intense colors, such as the blue of azulene or the orange of $\beta$-carotene.3
* Transition metals: Coordination compounds containing transition elements often exhibit color due to electronic transitions involving d-level atomic orbitals.2

Molecules that only absorb in the ultraviolet region appear colorless or white because they do not interact with visible light.23