The color of light reflected off a subject changes with the color of the main light source. The white balance setting on a digital camera adjusts the brightest part of a scene so it appears white. The human eye sees white objects as white regardless of the light source; unfortunately a digital camera does not.
Digital cameras are set to automatic white balance by default. Automatic white balance does a very good job under most circumstances, especially outside in good light. However, there are times when white balance needs to be changed manually to match the lighting in order to obtain more true-to-life colors in a photo.
Many digital cameras have a number of preset white balance settings as well as a custom white balance setting.
Preset white balance settings:
Daylight – for taking photos in direct sunlight
Cloudy – for taking photos on shady days, when skies are overcast
Fluorescent – for use under fluorescent lighting; your camera may have two fluorescent white balance settings
Incandescent/tungsten – for use under standard light bulbs and some types of fluorescent lighting
Flash - to be used in conjunction with the light produced by the built-in camera flash
Photos of a white door were taken under the same lighting conditions (standard light bulbs).
Automatic white balance was used to shoot the image on the left image.
Incandescent white balance setting was use for the image on the right.