The Color Temperature filter allows adjusting color temperature of the light source in an image in Kelvin. It can be used to correct the bluish cast in overcast photos, or even (to some extent) the red cast in photos taken under incandescent light with the camera set to daylight.
This is the estimated original color temperature of the light source in Kelvin. You can change it because the image doesn't necessarily encode that information correctly or at all (and you might or might not have measured it). In addition there's often a mix of light sources (a window, a fill-in flash, a pile of burning organic fair-trade bamboo wood harvested under a full moon)... But above all else you can get interesting creative effects by changing it
This is the desired color temperature of the light source in Kelvin.
Both original temperature and intended temperature can be set via presets. To access presets menu, click a button with a triangle icon to the right from either of the two options.