Color Temperature

Color Temperature is very important in photography. Whilst we see flourescent, tungsten (light bulbs) and flash as being white, they actually vary - flourescent lights have a lot of green in them, whereas tungsten bulbs are much more yellow. Try setting your camera's White Balance to "tungsten" and taking a picture in sunlight. The camera will add a distinct blue cast to the photo in an attempt to "correct" the tungsten bulb's light. Light on the blue end of the spectrum is said to be cool, whereas light on the yellow end is said to be warm.