Remember when you would create an indoor photo on your old film camera and it would come back from the processor looking orange (if you shot under incandescent lights) or greenish (if you shot under fluorescent lamps) ? The reason for this phenomenon was that the film you were using was made to create the most realistic color under outdoor lighting conditions and the lighting you were using didn't match daylight (see Tip #3 - The Color of Light
for more information).
Your modern digital camera makes this all obsolete right? Well... sort of. Digital cameras use a function called white balance to determine the color of the light in your photographic scene. In a nutshell, your camera looks for white or light colored objects, compares them to some fancy algorithms and quickly decides what your photo's color balance should be. If your scene doesn't contain a good reference for the camera, and maybe even if it does, the resulting photo will be off-color. I've seen estimates that the Auto White Balance feature is wrong 80% of the time. This number may be pretty darn close to the mark. Since Garbage In = Garbage Out, we want to make sure our photos are color balanced correctly the first time.
So, what to do?
You could just wait until after the photo is created and adjust the color in your photo editing software, but you'll end up doing this for every photo since white balance is determined as each photo is created, resulting in inconsistent color among your photos. Stay tuned... there are better ways...
In addition to an Auto White Balance mode, most digital cameras also allow the user to manually set the white balance using such settings as daylight, cloudy, fluorescent or incandescent. You can end up with pretty good results doing this, but you have to remember to change the setting whenever your lighting changes. And.... it's still not perfect. (If you use Nikon digital SLRs, I've seen at least one staunch advocate for using a Cloudy -3 setting for most daylight photos. I've used this setting on sunny days with very good results.)
A better solution is to use a white balance calibration target. These are carefully color-calibrated targets that you can use to get a perfect white balance every time. They are a little pricey in my opinion, but they are perfectly white and save a lot of time and trouble in post-production on the computer. At about $29.00, one of the lowest priced options is the Lastolite Ezybalance disc. This is a 12 inch disc (grey on one side, and white on the other) with a spring steel frame that allows the disc to be folded to 1/3 of its opened size. The grey side is handy for determining proper exposure (see Tip #1 - You Make Me Feel So Grey
Now, you might be thinking, why can't I just use a white piece of paper or cloth for a reference. The answer is .... because it's not pure white, despite what our brains are telling us. Most objects that we think are white have brighteners in them which are blue. Just for the heck of it I tried an experiment with a piece of white matboard I had around the office. I photographed a scene with the white matboard in it, then in Photoshop I used the matboard as the white reference to adjust the color Curves. Holy Bluishness Batman! Try it yourself.
If your camera has a manual roughly the size of a dictionary, it may also have a feature that allows you to use a photo as a reference for white balance. In that case, create a photo of your calibration target, then use your camera's menus to select the photo in memory as the white balance reference. Voila! All of your subsequent photos in this scene will be color balanced! Nice! ...just don't forget to create a new reference photo each time you change locations or lighting.