This is a non-mathematical survey of the basic sources of color. It does not dwell on the physiological and psychological perceptions of color. Modern color theory attributes most sources of color to the interaction of electromagnetic radiation with electrons. Listed are 4 groups of electron reactions and one of geometric and physical optics. The latter is divided into 4 categories: dispersion, scattering, interference, and diffraction. This article provides the conservator with information on the mechanisms which produce hard-to-restore colors, such as those found on some insects, lustrous ceramics, and as a result of scattering (i.e., blue sky, some colloidal colors). Materials used by the conservator in treating various artifacts fall into at least 7 of the 14 categories into which the 5 groups are subdivided. Most pigments are crystal field color; but Mars Black, lapis lazuli, and many dyes are grouped in transitions between molecular orbitals. Cadmium yellow, cinnabar, and metals are grouped in transitions between materials having energy bands. Colloidal colors and five pigments (e.g., 30 nm TiO₂) come under geometrical and physical optics (scanering).