Color temperature is the color degree of white light (warm look or cool look). Think of it as the opposite of Fahrenheit which gives you hot or cold to the touch. Lamp color temperature is measured in degrees Kelvin (K). The lower the color temperature, the warmer will be the look. The higher the color temperature, the cooler will be the look (or bluer). A standard incandescent light bulb is approx. 2700-2800K.
So, if you are replacing incandescent, look for an LED that is rated 2700-2800K for the same color appearance that you are replacing. If you are replacing halogen and want the same look, choose an LED that is 3000K (still warm, but slightly cooler than incandescent). If you want a cooler or bluer light, choose 4000K or higher which looks more like daylight.