sometimes the color is off so much in a photo that people look like oompa loompas from charlie and the chocolate factory. once in awhile your friends might end up looking like smurfs. what gives? the white balance is off. modern cameras do an awesome job of calculating white balance, especially when flash is used, but there are times when it can get messed up.
the way it works technically is that the camera (or computer if you're doing post-processing) does its best to pick what it thinks is supposed to be a neutral gray tone in the picture. once it determines that, it bases all of the other colors off of that gray tone. if the camera picks the wrong color for its nuetral gray, you can see why the colors would get skewed. here's the same photo with different extreme white balances:
color temperature : 2450K
color temperature : 10100 K
notice the labels on the pictures. white balance is measured on a kelvin
scale, which is a temperature. it's the same temperature scale on the boxes of fluorescent light bulbs at lowe's or home depot. the higher the temperature, the warmer the color (orange and red hues). conversely, the lower the temperature, the cooler the color appears (blue and greenish hues). a textbook photo has a perfectly balanced white point for true color reproduction. you can purposefully alter the white balance from its neutral point to emphasize something in the photo that you feel is there. color is a strong tool because it can evoke different emotions and feelings. subtle differences can make a big impact. take the next three photos for example. same photos, different white balances. do you see and feel the difference?
color temperature : 2850K
color temperature : 4550K
color temperature : 9900K
you can put white balance on auto mode or you can set it manually. even point and shoots will allow you to change the white balance, they just give it cute code names like "portrait, night scene, indoors, cloudy, etc..." on dslr cameras they just let you choose the color temperature.
i'm not going to delve into the jpg and raw shooting differences, but i do want to mention that if you shoot in jpg (all point-and-shoots force you to, dslr cameras give you a choice) then you cannot non-destructively alter the white balance in post-processing. you can change it slightly without noticeable degredation, but it's not the best. if you shoot in raw, you can use the entire spectrum of color temperature during post-processing in a non-destructive manner. there are reasons why but i'd hate it if my blog readers were all passed out in front of their computer because i started talking about image compression.
next up: resolution