When it gets really dark, we use the expression “pitch black”. As photographers however, we need to remind ourselves that black is not a color at all. Black is the total absence of light, and color is all about light. Without light, we see no colors at all.
The same goes for white, which is not a color either. White is simply a complete mixture of all visible colors. Our mind tells us that the objects that we desribe as “white” are always white, but they’re really not. Their apparent color varies depending on the light source that they are reflecting.
The type of light around you will alter the colors you see and those that your camera will record. That’s why you need to consider white balance when you want to control the color rendition of your photos.
A large spectrum of light can be perceived by the human eye and the sensor of a digital camera. The type of light source will affect both your eyes and the camera, but not to the same degree.
Cameras need a white reference to reproduce the colors you see in the pictures you take. Your brain does it all the time. Of course, you don’t even notice.
The camera’s automatic white balance performs well in most situations. But when you have to match specific colors in your photos, you’ll need to choose carefully.
Once you are out of AUTO mode, most cameras offer settings for daylight, shade, flash and a few of the most common sources of artificial light. You can also set your camera by showing it a “reference” white, such as a white piece of paper or even a photographic gray card. If you need to be really accurate, you can use a color meter to measure the light and set it precisely based on your reading.
In everyday shooting, you just need to pay attention to light sources. If you want to take a picture indoors with daylight coming through windows, a lamp "warming up" a table and fluorescent tubes on the ceiling, you and your camera will have to juggle with three light sources that stand at different color temperatures.
Unless the first image you take is extremely satisfying, now is the time to try these different white balance settings on your camera. Go ahead and experiment.
You can always set white balance for your main subject and forget the rest, which would be the most accurate, but forgetting the rest comes at a cost: you might get surprises that you won’t like. Sometimes AUTO is still the best compromise.
Otherwise, you may want to try and set up your shots so you have only one light source, which makes it all simple.