This chapter explores some of the sources of color. Light can interact in other ways with bulk matter, and this can also lead to color. Thus far, the processes giving rise to color have involved absorption or emission of light. However, there are other physical interactions that give rise to color by change in the direction of the light. Refraction results from the change in speed of light when passing from one medium to another. When a uniform, nonabsorbing medium, such as air or glass or salt, transmits light, the photons are absorbed and immediately re-emitted in turn by all the atoms in the path of the ray, slowing down the light. Light travels fastest in a vacuum, and more slowly in all other materials. Light travels faster in air than in a solid. The color-matching of the chameleon to its environment is largely a result of light scattering.