This chapter looks at colors and luster in metals and origins of color in semiconductors. In both metals and semiconductors, very large numbers of atoms are usually required for the presence of color. Two processes are taking place here to increase the luster and color intensity of the polished wood: a reduction in diffuse refection from the outer surface and introduction of multiple reflections under the polish. However, the polished surface is much flatter, so it will reflect primarily at a particular angle giving the wood its luster. The color of the polished surface also is more intense because the colored light from the rough wood surface will not be polluted with diffusely scattered light. The polish layer also allows multiple internal scattering of the light. The transmission will vary with the wavelength of the light, and such transmission can give rise to color. The color of heating coil in a toaster dies off slowly when the toaster is unplugged.