In short, color temperature is how color will appear when it’s measured at a certain temperature using the Kelvin scale. If we have an ideal blackbody that can spontaneously heat up, when it reaches certain temperatures it will start to radiate light in different colors based on the temperature, from red to orange, orange to yellow, yellow to white, and white to blue. And we use the Kelvin scale which starts from absolute zero to measure the temperature (since 0 Kelvin is absolute zero, 273.16 Kelvin equates to 0 degrees Celsius and 32.018 degrees Fahrenheit).