Photoxels has a nice tutorial on White Balance.
If you come from the world of films, you may remember using filters to correct for incandescent or fluorescent lighting. Most people don’t bother and their indoors pictures invariably come out with a yellow/orange or bluish cast. In the digital world, these correction filters are no longer necessary, replaced by a feature found in most — even the entry-level — digital cameras called, “White Balance.”
Link via PhotographyBLOG
