Most of us take white balance for granted. We trust the camera to get the color right for us in almost all our photos. When a subject is illuminated by light, its color is impacted by that of the illuminating light. People see a sheet of paper as white, regardless of whether it is illuminated with daylight, tungsten light or fluorescent.
White balance is the process the camera uses to give a good representation of the subject under a variety of light sources. When there are multiple light sources influencing the frame, the process becomes much more complex. A portrait by a window might have warm tungsten light in the room, daylight from the window and a flash on the camera all illuminating the subject with different colors of light.
