If one can answer the question “Why is the sky blue?” you’re already half way toward understanding the need to White Balance your camera. The answer is that sunlight is blue. We see the color of the light because it is reflected back to us from particles in the atmosphere.
The second half of understanding White Balance comes from the follow-up question: “If sunlight is blue, why doesn’t a white object illuminated by sunlight look blue?” The answer is that your eye tricks you into seeing white as white even if they color of the light is blue.
Light from different sources have different color qualities. The color quality of light can be measured in degrees on a scale called the Kelvin scale. The Kelvin scale is also used for temperature, which leads to some crossover in terminology from color. Hence, the measurement of the color quality of light is also referred to as “color temperature”.
Please have a look at the chart below. This chart is a representation of light on the Kelvin scale with different light sources represented with their relative color temperature. Please note that the color temperatures of various light sources are approximate.