We live in a rainbow of colors. You may not notice this rainbow, but all the same, it's there. Every scene features objects illuminated by light that's slightly blue, green, pink, orange, yellow, or another color. Contrary to what we seem to see, light is rarely crystal clear and colorless. We only think the light is colorless because, when we view such scenes, our eyes naturally compensate for the various colors of light, without even thinking about it.

Our cameras, on the other hand, don't have it so easy. They don't necessarily know how to automatically compensate. When presented with an overall yellow light, for example, cameras will simply render the scene with a yellow cast. When the light is slightly blue, cameras will render the final image slightly blueunless we set the camera to do something to change this.
The process of compensating for color tone in light is referred to as balancing the light or, simply, white balance. A bit of blue added to overall yellow light will balance things out; a dash of yellow added to blue light, will result in clear, balanced light. All the colors in that image will look natural and realistic. Similarly, adding red to a photo with a blue cast and red to a photo with a green cast will produce images with clear, realistic colors.

In order to balance the color of light, the camera has to first find what is called the white point. This is the point at which a white object within a photo would be rendered as pure white. When there's no white object, a best guesstimate has to be made. While most digital cameras will gladly try to do this guesswork for you, automatically determining white balance by scanning the image for a white point, it's not wise to rely on these automatic white balance modes all the time. Just as with exposure, there will be times when the camera's automatic functions lead you astray. At these times, you'll want to know enough about white balance to manually adjust the settings until you get natural, clean, and realistic colors.

This is especially true if you photograph scenes that are bathed in a particular color. For example, if you're photographing a mountain peak radiating pink in the aspen glow of a summer evening or a person's face bathed in the beautiful light of the sunrise, the automatic white balance will often defeat the purpose. Wrongly identifying these warm tones as an unwanted color cast, the white balance will likely compensate enough to cause this interesting light to disappear. The idea is that you want to balance the whites in your image; you want your image to be not too pink, not too blue, not too green . . . but rather "just right."