White balance (or WB) is necessary in digital cameras because light doesn’t just vary in brightness but also in ‘colour temperature’. The human eye naturally adjusts for this (making a sheet of white paper appear white no matter what the lighting conditions) but the camera requires WB to compensate for these different conditions. Generally the Auto White Balance (AWB) setting does a good job in getting the colour correct in your photos but like many automatic settings, is not foolproof. Also, the AWB only operates between a confined range of colour temperatures (3000 – 7000 Kelvins). It may struggle for example, taking a picture of a floodlit building or, on a foggy day.
Your DSLR has a number of presets designed for specific light sources to try to help you:
Tungsten (normal light bulb) 3200K
White fluorescent 4000K
For greater control of colour temperature use the Custom White Balance setting which provides a range from 2000 – 10000K. To do this take a picture with a piece of white paper in the centre of the frame. Press the Menu button & search for Custom White Balance, then press Set. The reference picture should be shown on the display. Press Set once more. Your new custom white balance is now created. Select the CWB option & take the actual shot.
If you shoot in RAW it is possible to alter the WB in the editing stage.
Getting the WB wrong on purpose can create some artistic shots. For example, set WB to “cloudy” with an outdoor subject lit with sunlight on a bright day & the picture will have a warmer tone (good for portraits or architecture). Sunsets can look more impressive with WB set to “shade” & landscapes obtain a moonlit look with a “tungsten” setting.