Differing light sources produce light of varying colors. Unlike the human eye, your camera
doesn’t have a concept of what color certain objects or subjects should look like and so doesn’t have an ingrained ability to edit for color accuracy. Instead, all it can do is analyze your photograph, determine what the most predominant color is within the frame, and assume the light source has something to do with that color.
This leaves the color accuracy of your photography vulnerable to mistakes of analysis and color averaging. Trying to correct for this imbalance is a setting in your camera called white balance.
Your first issue arises when your camera mistakes the actual color of a subject for the color
of light on that subject. This happens to some extent whenever your camera uses the automatic white balance setting. Here it simply analyzes the scene and corrects the whole frame for what it feels is the color of the light source. In some situations this comes close, in some cases not so much. Let’s look at some examples.
Here I shot a picture in auto white balance, it doesn’t look too bad. But this part of the yard
was in shade, so I changed my setting from auto to shade.
Color here renders more accurately. And the difference jumps out, doesn’t it? The snow is noticably whiter. This is the power of your white balance settings. Behind auto you’ll find sunny day, shade, cloudy day, florescent, incandescent, flash, and a customizable setting. You’ll know immediately if you’ve left your white balance on sunny day and then shot in a picture in the shade. It looks like this.
But now we come to another difficult situation. What if part of the frame has one color
temperature and another part is different? For instance, in another part of the yard there was
open daylight, but behind it was shade. If we shoot this scene in auto we wind up with this
Neither part of the frame is really correct. But if we are shooting in JPEG there isn’t much
else we can do. Here is the same shot in sunny day white balance.
Notice how the whole frame is cooler in color temperature, more blues and greens. When
the camera tries to correct for warmer colors (as it would if sunlight was the predominant light
source) it adds cool ones. The opposite is true if the predominant light source was shade. The
camera will add warm tones (reds, oranges, yellows) to compensate. So here is the same shot, but with white balance set to shade.
In the previous picture the snow was rendered correctly and the background was too cool.
Here the background is accurate, but the snow and the base of the tree are too warm. How can we correct for this issue? After all, the world is full of mixed lighting situations.
There are really two options available to the modern photographer. The first is to use auto
white balance while shooting JPEG and accept that it won’t be perfectly accurate. The second is to shoot in RAW rather than JPEG. In RAW your camera records all color data and you
maintain a complete capability to edit individual areas of the shot (this is called local adjustment, asopposed to global) and create accurate final products. In fact, your ability to edit color accuracy is one of the primary reasons photographers love shooting in RAW.
For now, at minimum you should take advantage of your white balance presets. Soon there will be an update to explain how the presets (while better than auto, certainly) still are not as accurate as many photographers would like.