The colour temperature of light is measured in degrees Kelvin (after the physicist Lord Kelvin). An incandescent lamp emits light with a warm temperature of 2800K, whereas direct sunlight has a cooler colour temperature of around 5000K. Capture NX-D has a colour-coded slider based on the Kelvin scale. You can slide it to the left to cool down a shot, or right to warm it up. Some of the white balance presets in the drop-down menu also refer to a precise Kelvin value (such as Fluorescent 3000K).