We describe the color of light in degrees Kelvin.
Take a look at the white balance settings on your camera.
Those white balance settings represent the Kelvin temperatures of different light sources.
The settings probably look like icons but those icons are associated with a type of light and that type of light is associated with a Kelvin number.
The Kelvin scale goes from red to blue.
The lower the Kelvin temperature the redder the light source.
The higher the Kelvin temperature the bluer the light source.
Want to see this in action? Take a good look at a flame. The hottest part of the flame is the bottom of the flame. Whether it be a candle flame, a match flame or the flame on your gas stove the bottom part of the flame is blue. As the flame fans out it gets cooler and redder. Probably not red, but the color yellow or orange is a shift in the red direction of the Kelvin scale.
When your camera is set to auto white balance, your camera picks a white balance setting for you.
When you pick the white balance setting you can begin to get predictable color shifts based on the relationship between the white balance setting on your camera and the color temperature of the light source. This use of color in this manner adds more depth to your compositions.