White balance is one of those settings on the camera that no one really knows much about, particularly since there's an "automatic" option on the dial. Most of the time, setting your white balance to automatic is acceptable, particularly if you're editing your photos after you take them and can adjust colour as needed. Adjusting colour in post-processing can be a lot of work, though, and you may find that your camera can help you out a little bit if you adjust your white balance settings.
What is white balance? An easy definition is this: a setting on your camera that allows it to adjust for the different colours of light that are emitted by different light sources.
Ever wondered why your skin looks less than spectacular when standing under the fluorescent lights in a fitting room? It's because of the colour cast given off by the fluorescent light. All light, including sunlight, emits some sort of colour. Our eyes process this without much difficulty; our cameras, however, see things differently. The white balance setting acts as a filter over what your camera thinks it is seeing.
I took the following photos on a white sheet of paper on top of my kitchen counter, under our pot lights. The house was quite dark today, so there wasn't really any natural light interfering with the picture, and I did not use my flash. I changed my white balance setting each time and you can see the impact it has on the colour of the photographs.
Auto White Balance (shown as AWB on your camera): Generally speaking, the camera did a good job (particularly when you see what happens with some of the other settings). It still is a bit too pinkish-gray for the background, which should be almost white.
Sunlight or Daylight (symbol of a sun): Definitely not the right setting for this photograph, but that's not a surprise, given that I took the photo inside a relatively dark room. Great idea to use this on a bright and sunny day.
Shade (symbol of a house with shade): There's a whole lot of extra orange added on this setting, which is great if you're actually using it in the shade, since shade can be quite blue.
Tungsten (symbol of a light bulb): Probably the closest lighting source to what we have in our kitchen. Not bad, but not great. Very close to the automatic setting.
Fluorescent (symbol of a fluorescent tube): You can see that this filter brings more pink into the picture, which would counteract the greenish tinge given off by most fluorescent lights.
Flash (symbol of a lightning bolt): The flash on your camera will usually cast a cool light on the subject, so this orange warms it back up. (Remember that I did not use my flash for these photographs, which is why this setting didn't work for my picture.)
Custom (a square and two triangles, almost looks like a flower): Some cameras, like my dSLR, have the ability to choose a custom white balance. First you take a photograph (in the same lighting conditions as your subject) of a white piece of paper, a grayscale card, or you can use an Expodisc (which was my choice). You then set your white balance to custom, and direct the camera to use the information from that image to set the white balance. It gave me the most accurate results:
Colour is measured by the Kelvin temperature scale, and many dSLRs will also let you choose a specific colour temperature on that scale. I'll admit that I just don't go that far when I shoot. Most of the time, I'm just grabbing my camera and shooting on AWB—I'm lucky if I'm fast enough to catch the kids doing what I wanted to capture. I do, however, tinker with my white balance when I have a bit more time. I find that the minute or two it takes me to set a white balance saves me half an hour (or more, depending on what I'm shooting) in post-processing.
Play around with your white balance, and experiment. Sometimes you may purposely choose the "wrong" white balance setting to achieve a different feeling in your photograph. Do what works for you!
Looking for some photography help? Check out the other Photography 101 posts.