White balance

Today I am going to talk about white balance.
Lot of people always use the camera with white balance set to "auto", and this is not the best option.
First at all, what is WB?

color balance is the global adjustment of the intensities of the colors (typically red, green, and blue primary colors). An important goal of this adjustment is to render specific colors – particularly neutral colors – correctly;

Wikipedia
Why it is necessary to set white balance? Because different lights have different colors. For example, the incandescent lights (normal light bulb) are orange, or fluorescent it’s green!. With WB we can set photography colors to the correct colors, regardless of the lighting color.
Because of that, normally it’s not a good idea to mix different kinds of lights in the same photo. (We have just one WB).
Perhaps you have seen a photographer take a picture of a grey sheet. That’s because another option is to set the white balance later. If you shoot on RAW format, camera is not going to apply any WB to the picture and you will be able to do it later. With that grey sheet, programs like Photoshop, can compare the grey with a real grey in the picture and identify the color of the lights.
WB has a lot of creative possibilities. Perhaps you don’t want true color - perhaps you are looking for something different. Have you seen pictures with a blue background? This is very easy to do. You just have to set WB to tungsten and sun light will look blue! If you are lighting your subject with an orange light (like a bulb light or a flash with a CTO gel) the subject will be in genuine colors).